Solarized Sublime Sekai

Optimisation d'une VM GCP et domptage de Neovim

Thu, 12 Mar 2026 00:00:00 +0000

Aujourd’hui, j’ai passé ma configuration de développement sur une VM Google Cloud Platform (GCP). Entre les contraintes de ressources de la machine et le peaufinage de mon environnement Neovim pour mon projet Rust, voici ce que j’ai appris.

1. Transfert de fichiers avec rsync

Pour uploader mes dossiers de projet vers la VM, j’ai utilisé rsync. C’est bien plus efficace que scp car il ne transfère que les modifications.

rsync -avzLP --exclude='.git' \ 
  ~/.local/share/typst/packages/preview/auto-mando/ \
  user@$(gcloud compute instances describe typst-bot-vm \
    --format='get(networkInterfaces[0].accessConfigs[0].natIP)' \
    --zone='us-east1-d'):~/

Le « combo doré » :

Rust Project Structure for rust-canto

Sat, 07 Mar 2026 01:13:26 +0100

Background

I created my first crate rust-canto even though I didn’t know Rust, so that I can bring automatic Cantonese word segmentation and romanizations into Typst.

This is a great idea. Moving from a complex xtask workspace to a streamlined build.rs and build.sh workflow is a common evolution for Rust projects, especially when targeting WebAssembly.

Five lessons learnt from chat bot

1. Avoid the “Crates.io Path Dependency” Trap

The Problem: Using a Workspace with a local helper crate.

Typst Package for Jyutcitzi

Sun, 08 Feb 2026 17:09:59 +0100

Background

As a native Cantonese speaker, I found it inconvenient to repeat all the time when I have to teach others how to speak my language. I acquired Jyutping (粵拼) a couple of years ago. It’s a popular phonetic system for the Cantonese language. However, some of my fellow countrymen aren’t fond of this romanization scheme.

A soft “introduction” to “Introduction to Jyutcitzi”

Recently, I’ve heard of another phonetic system called Jyutcit (粵切). It’s basically a “cutting sound method” (切音法). Each syllable is “initial + final”. To compose a sound, we take two syllables, from which we keep

Imprimante HP Deskjet 4100 sous Linux

Fri, 23 Jan 2026 18:31:59 +0100

Introduction

J’ai récupéré une imprimante HP DeskJet Plus 4122. Je m’en rarement servais car je pensais à tort que HP ne marchait que sous Windows. J’aime tellement Linux que je me connectais pas souvent à Windows, où l’appli HP Smart est bloquée de temps en temps.

Cet après-midi, après une petite recherche, je me suis rendu compte qu’il y avait une pilote HP Linux Imaging and Printing (HPLIP) pour Linux. J’ai décidé de l’essayer sur mon système Lubuntu 24.04.

Choisir La Stabilite en Christ

Mon, 25 Aug 2025 16:23:12 +0200

Hier, lors de la prédication, j’ai reçu un message très important. Nous avons toujours le choix : celui de refuser d’être blessés, affaiblis ou angoissés par les erreurs de nos parents, par les pensées négatives ou par les relations toxiques.

Une sœur de mon église m’a partagé que la stabilité émotionnelle n’est pas quelque chose que l’on construit seulement par soi-même, mais un don de Dieu. En effet, pour ne pas être détournés par ces pensées destructrices, nous devons nous rappeler que nous sommes d’abord enfants de Dieu. Il est notre Père, et Son amour est inébranlable et inséparable, aussi longtemps que nous plaçons notre foi en Lui.

Plus grande chute du plus grand royaume

Sun, 10 Aug 2025 14:29:12 +0200

Lors du culte la semaine dernière, la pasteur a prêché sur l’histoire du roi Salomon, qui avait demandé l’intelligence pour exercer la justice, qui l’a reçue. Son royaume était le plus riche, le plus puissant au monde, et aucun pays ne peut le surpasser, ni ceux d’avant, ni ceux d’après.

En voyant un verset du livre des Proverbes pertinent, la foule a réjoui. Cependant, je me suis mis en doute au sujet de la chute de son royaume après sa mort. Salomon a-t-il reçu ce qu’il avait demandé ? Une chaîne de raisons est sortie de ma tête :

Dix Pensees Formidables Chretiennes

Sun, 27 Jul 2025 17:37:42 +0200

Ma prof m’a envoyé dix citations remarquables il y a des années. Un autre blog d’une écrivaine a inclus une autre qui n’est pas dans le premier.

SE SOUCIER, n’enlève pas LES SOUCIS DE DEMAIN; ÇA NE FAIT QU’ENLEVER LA PAIX D’AUJOURDHUI!

Tikz Loop Over Coordinates

Mon, 07 Oct 2024 14:50:36 +0200

This is my belated response to a self-identified dupe on TeX.SE.

Background

The list in a \foreach loop is often long.

\foreach \pointA/\pointB in {{(1,0)}/{(2,2)},{(3,4)}/{(2,1)}} {
  \draw \pointA -- \pointB;
}

Imagine having several other loop variables. The code inside the {…} list won’t be readable.

Problem

How can I make it looks smarter?

\foreach \pointA/\pointB in {
  {(1,0)}/{(2,2)},{(3,4)}/{(2,1)}
} {
  \draw \pointA -- \pointB;
}

doesn’t work.

Inspiration

Recently, I was asked the way to make two graphs to illustrate a complex function.

Upgraded to Hugo v0.135

Mon, 07 Oct 2024 13:05:16 +0200

Background

18 months ago, I used latest Docker image in GitLab container resgitry for Hugo extended at commit 168fe3d.
Six years ago, I integrated static comments to this blog.
Last week end, when my friend tested static comments here, she reported that @StaticmanLab’s GitLab token had been expired. As a result, I updated it and re-deployed my Staticman instance.

Problem

I wrote a sample comment containing math equations to test if it’s still working. The back-end processes were fine, but the site rebuilding wasn’t successful, as commit c531a0b reveals.

Exponential Function Series Definition

Sun, 08 Oct 2023 16:50:58 +0200

Motivation

My previous post about the definition of the exponential function has provided no connection between a well-known characterization (or an alternative definition) of the exponential function:

$$\exp(s) = \lim_{n\to\infty} \sum_{k=1}^n \frac{s^k}{k!}.$$

The term to be summed is simpler than the one in the binomial expansion of $(1 + s / n)^n$.

Solution

We want this sum to be as small as possible as $n \to \infty$.

$$\sum_{k=2}^n \left( 1 - \frac{n \cdot \dots \cdot (n + 1 - k)} {\underbrace{n \cdot \dots \cdot n}_{n^k}} \right) \, \frac{x^k}{k!}$$

Observe that the fraction is a product

Start Oracle From Git Bash

Wed, 07 Jun 2023 09:36:40 +0200

Goal

To run Oracle SQL in Git Bash.

Assumption

You have sqlplus added to your PATH.

export PATH=${PATH}:/c/oraclexe/app/oracle/product/11.2.0/server/bin/

Problem

The option /nolog doesn’t work as expected.

$ sqlplus /nolog

SQL*Plus: Release 11.2.0.2.0 Production on Mer. Juin 7 09:43:47 2023

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

…

When SQL*Plus starts, and after CONNECT commands, the site profile
(e.g. $ORACLE_HOME/sqlplus/admin/glogin.sql) and the user profile
(e.g. login.sql in the working directory) are run.  The files may
contain SQL*Plus commands.

Refer to the SQL*Plus User's Guide and Reference for more information.

Solution

Luckily, googling “start sqlplus from git bash”, I found the solution in this related Oracle Forum post: using an extra slash will do, i.e. sqlplus //nolog.

Closer Look into ArrayList Iterator

Sun, 07 May 2023 15:17:57 +0200

Background

Given an ArrayList of Integers from 0 (inclusive) to 10 (exclusive) with step size 1. We use a while-loop and an Iterator<Integer> to check if this ArrayList hasNext() element, before we remove() the current element.

Problem

The code below throws an IllegalStateException.

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class UnderstandArrayListIterator {
    public static void main(String[] args) {
        List<Integer> a = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            a.add(i);
        }
        Iterator<Integer> iter = a.iterator();
        iter.next();
        while (iter.hasNext()) {
            iter.remove();
        }
    }
}

Discussion

After invoking remove(), lastRet is set to -1, so next time that this method is invoked, the condition lastRet < 0 in the if-block is satisfied, resulting in an IllegalStateException.

Notes du Jour

Thu, 20 Apr 2023 22:26:41 +0200

Dans le classique schéma pour la gestion du projet, on met le besoin du client d’abord. C’est important de l’entendre avant de commencer le traf. Sinon, on risque de perdre des heures (ou pire des jours) sur une chose que le client ne valide pas. Avant d’y mettre l’effort, il est bon de lui montrer idée générale et de lui demander un avis, afin d’éviter de lui délivrer un produit qu’il ne veut pas.

Passed Codingame Java Certification Test

Thu, 20 Apr 2023 10:04:14 +0200

String regex replace using capture groups

Since Java SE 9, java.util.regex.Matcher’s replaceAll() method supports lambda expressions.

// import java.util.regex.*;
String varName = "random_string";
Pattern pattern = Pattern.compile("_([a-z])");
Matcher matcher = pattern.matcher(varName);
String result = matcher.replaceAll(m -> m.group(1).toUpperCase());

Source: Arvind Kumar Avinash’s answer on Stack Overflow

Check characters properties using `Character`’s static methods

The Character class provides some static predicates like

isAlphabetic(char c)
isDigit(char c)
isLowerCase(char c)

Source: Java Character isAlphabetic() Method on Javapoint

Notes pour l'algo des tableaux

Tue, 18 Apr 2023 09:17:31 +0200

Lien vers le diapo

Notes d'algo du jour

Mon, 17 Apr 2023 09:58:58 +0200

Lien vers le diapo

Diapo Sur HashMap

Thu, 13 Apr 2023 14:55:16 +0200

Lien vers mon diapo sur HashMap

Visual Studio Code

Wed, 12 Apr 2023 22:51:53 +0200

Usual keys

I’ll only list those I find useful.

<C-Up> / <C-Down>: move up ↑ / down ↓ without changing cursor position.
<C-g>: go to line number.
<C-p>: go to other files.
<C-S-p>: show Command Palette.
<C-b>: toggle left side bar.
<C-j>: toggle Terminal.

Searching / Replacing

As usual, it supports custom selection range and regular expressions as expected. Transformations preserving cases are possible.

Fixed Archetype Error for This Site

Tue, 11 Apr 2023 15:51:05 +0200

Background

In Customized Archetype for This Site, I was using

{{ slicestr .Name 11 | humanize | title }}

in the title attribute in my site’s archetypes/default.md, so that the first 11 characters (YYYY-MM-DD-) would be taken out if I type this command.

$ hugo new post/$(date -I)-<MY_POST_TITLE>.md

In practice, <MY_POST_TITLE> can be replaced to any title, like my-post-title.

Problem

I wanted to create my IntelliJ cheatsheet, so I typed this command.

IntelliJ

Tue, 11 Apr 2023 15:48:55 +0200

The following shortcuts are based on M$ Windows.

<C-Up> / <C-Down>: move up ↑ / down ↓ without changing cursor position.
<C-Alt-↑> / <C-Alt-↓>: open file explorer for the project root.

Searching / Replacing

As usual, it supports regular expressions as expected.

<C-F>: search
<C-R>: replace
<F3>: jump to next matching word
<S-F3>: jump to previous matching word

Editing / Selection

Syntax-independent shortcuts:

Exploration of My First IntelliJ Project

Wed, 05 Apr 2023 09:46:00 +0200

We’ll try to stay in the project root if possible.

Find all non-hidden files to know the file structure.

$ find -path './.*' -prune -o -type f -print
./Algo-init.iml
./out/production/Algo-init/fr/eql/ai114/algo/init/demo/_1_HelloWorld.class
./src/fr/eql/ai114/algo/init/demo/_1_HelloWorld.java

-prune returns true for the chosen path and prevents find from descending.
-o means OR, so the paths matching -prune won’t pass through -o.
-type f selects files, not folders.
By default, AND is used to connect different conditions.

Reuse Commands with Shell Arguments

Sat, 25 Mar 2023 11:23:58 +0100

Background

We often want to test the output with different values for a parameter. Here’s an example: we have a parameter that pandoc uses to / compile source code files to PDF / M$ Word / etc.

rm output.html; param=0; pandoc input$param.txt -o output.html; \
echo param = $param

In practice, a parameter can be a font, the font size, etc, and there can be multiple parameters.

Finding Pandoc Logo

Fri, 24 Mar 2023 02:10:45 +0100

Background

I’m writing my guide for preparing simple documents. I hope that users can prepare documents efficiently and the prepared documents look smart.

Problem

To help readers get my message in the linked guide, I used many icons from Font Awesome. However, it doesn’t include pandoc’s logo. I tried searching that using the search string “pandoc logo filetype:svg”. Duckduckgo couldn’t find any results. Luckily, Google found many SVGs. The first result linked to a relevant discussion on Google Groups. However, all posts were collapsed, and the desired SVG didn’t show up.

Simple Document Templates

Wed, 22 Mar 2023 12:32:10 +0100

To get started

Download FOSS (free and open source) tools:
- $\LaTeX$: a typesetting system often used by academians and researchers. It gives documents with a more impressive appearance.
  - Windows: Mik$\TeX$ → click Download in the navbar
  - Linux: install $\TeX$ Live directly from the TUG ($\TeX$ User Group)
  - Mac OS: Mac$\TeX$ (I’ve never used that.)
- pandoc: a document markup language converter (e.g. ↔︎ , $\LaTeX$ ↔︎ , → )

Some Public APIs to Be Viewed

Thu, 16 Mar 2023 12:29:56 +0100

API	description
JSON Placeholder	mock REST APIs for development only
Google Translate	generate free translations up to a certain limit
Open Weather Map	weather prediction across the world
REST Countries	info about the world’s countries
IP API	data about IP addresses
Random Data API	like the first one, but with a sharper focus on random data
Pokemon API	info about Pokemon with recent introduction of GraphQL API

Merge Two PDF to Single Encrypted PDF

Wed, 15 Mar 2023 17:47:14 +0100

Problem

I have unprotected

input1.pdf
input2.pdf

and I want to create one single encrypted.pdf.

My try

I looked up QPDF’s manual and tried the following command.

qpdf --empty --pages input{1,2}.pdf --encrypt upw opw 256 -- encrypted.pdf

but I got this error.

qpdf: unrecognized argument --encrypt (pages options must be terminated with --)

For help:
  qpdf --help=usage       usage information
  qpdf --help=topic       help on a topic
  qpdf --help=--option    help on an option
  qpdf --help             general help and a topic list

Solution

The sentence inside the parentheses says it all.

How to Start an Online Empire Without a Job

Tue, 14 Mar 2023 16:31:20 +0100

Difficulty

To start an online empire from zero is not something that can be done easily. One lacks the connection with experienced netizens who might know the inside secrets.

Solution

You may start your empire on Forge of Empires. You’ll be guided by a beginner-friendly tutorial. The daily tasks are easy and they will only take you a few minutes, but they are rewarding. You’ll end up earning thousands of coins on the website.

Ten Probably Handy Sites

Fri, 10 Mar 2023 09:34:13 +0100

A brief summary of 10 Incredibly Useful Websites on Medium.

Upword.AI (paid): summarise stuff
Gamma (free trial for the moment): get professional slides in min, not open source
IMGCreator (free, point-based): text/img → img, chatGPT powered
Popsy (free to create, paid to publish): no-code website buider
Visual Capitalist (free): explanatory charts
TypeLit.io (free for some œuvres, paid for own book): type classics out to train typing
Zorp.one (free for trial, paid for deploy): no-code app generator for businesses, e.g. delivery, store management, doc collection
Kialo (free): repository for debate arguments, with discussion topology
Nomad List (free limited trial, paid content): good for remote workers, find remote work opportunities, insights into cities, dating app (that I don’t recommend)
SuperMeme (paid): AI meme generator

Encrypt PDF on Command Line

Sat, 04 Mar 2023 14:45:05 +0100

Background

On M$ Win*, I don’t have dedicated PDF readers like Adobe.

During visioconference, one might want to share some downloaded PDFs. Those documents can be part of an ebook or notes. In some situations, they can provide context to a discussion.

Problem

Under the same folder, you might have

downloaded_ebook.pdf
personal_info.pdf
other_personal_stuff.pdf that you don’t want to expose while streaming.

However, each downloaded PDF usually comes with a name set by others. It can be tedious to rename them according to your own habits. To protect users’ privacy, we can

Adjust Git Bash Font and Window Size

Sat, 04 Mar 2023 14:16:58 +0100

Goal

Make the characters larger and more readable.

Solution

The option names might be found in the manual. Sometimes, I find opening MINGW’s settings through GUI helpful.

FontHeight=12
Columns=143
Rows=36

I’ve read Gerald Lee’s .minttyrc. I’ve enlarged the window size so that in the standard output, one line can contain more info.

Fujitsu LH532 Thermal Paste Application

Wed, 22 Feb 2023 16:40:10 +0100

Background

My old laptop was bought ten years ago. I had never changed the thermal paste between its CPU and its fan. As a result, it had been getting hot during my online tutorials.

Photos

thermal paste on CPU displaced after ten years

thermal paste on fan displaced after ten years

dried thermal paste cleaned and removed

with isopropyl and kitchen towel

Removed jQuery Dependency from My Math Editor

Wed, 19 Oct 2022 23:06:10 +0200

Background

jQuery provides many handy functions to speed up the development, for example document.ready(), element.toggle(), element.hide(), etc. My math editor used some of them. However, I replaced them with Vanilla JavaScript at commit 4a35c45b.

Goal

Some users complained about the white background in the past versions of my editor. That had motivated me to refactor the code, so that it would be easier to maintain and to add in new features.

HTML5 input types used

Actual appearance might vary across browsers.

Showdown KaTeX With mhchem

Tue, 18 Oct 2022 13:46:01 +0200

Background

I’ve written about bringing user-defined KaTeX macros into Hugo a few years ago. Looking back, I realized that I only knew how to copy code at that time.

Goal

To replace the current code for my math editor with Showdown-KaTeX.
To bring mhchem into my LaTeX + Markdown sandbox.

Motivation

To get the benefits of the three free (as in “freedom”) technologies.

Markdown syntax is (much) simple(r than its LaTeX equivalent, especially for tables, ordered/unordered lists, etc).
LaTeX syntax for math is, in the long run, worth learning, so that your fingers can stay on the keyboard while editing math expressions.
mhchem allows writing chemical equations conveniently as in the previous point.

However, Rattle has pointed out the difficulties of mixing LaTeX and Markdown syntax. In his proposed solution for WordPress, he first renders KaTeX before moving to Markdown. He has provided an example use case with a dollar sign $ in a normal Markdown content (e.g. An apple costs $1.5.)

Exponential Function Product Rule

Mon, 19 Sep 2022 14:23:17 +0200

Motivation from compound interest

Increase the number of times that the interest is compounded each year ($n$), so as to increase the final amount of money ($A$)

$$A = P \left(1 + \frac{r}{n}\right)^{nt}.$$

$t$ and $r$ are the number of years and the interest rate per annum.

As $n$ becomes large, we can approximate the amount by

$$A = P e^{rt}.$$

The value of $A$ in the above formula is the amount compounded continuously.

Existence of Four Triangle Centers

Sun, 18 Sep 2022 12:14:55 +0200

Settings

Let

$P$ be an arbitrary reference point.
$\triangle ABC$ be a triangle.
$\vec{a} = \overrightarrow{PA}$, $\vec{b} = \overrightarrow{PB}$, $\vec{c} = \overrightarrow{PC}$

Remark: $O$ is reserved for circumcenter.

symbol	name	meaning
$G$	centroid	center of gravity
$H$	orthocenter	three “heights” are concurrent
$I$	incenter	center of inscribed circle
$O$	circumcenter	center of circumscribed circle

Centroid

Verify that $(\vec{a} + \vec{b} + \vec{c})/3$ satisfy the constraints.

Orthocenter

Let

$H$ be the point of intersection of two altitudes $AA_H$ and $BB_H$
$\vec{h} = \overrightarrow{PH}$

\begin{align} (\vec{h} - \vec{a}) \cdot (\vec{b} - \vec{c}) &= 0 \\ (\vec{h} - \vec{b}) \cdot (\vec{c} - \vec{a}) &= 0 \end{align}

Add these two equations together.

Katex Boxed Equations

Wed, 07 Sep 2022 01:39:20 +0200

Goal

To render a bordered box with multiple equations.

Background

My previous article about dot products contains some boxed math expressions: some are inline and some take up the whole line.

For inline math, that’s simple: either $\fbox{text}$ or $\boxed{a=1}$ will do. For displayed math, these two KaTeX commands will ignore the newline command \\.

Solution

A simple Google search ‘“katex” AND “box”’ saved the day. It led me to this relevant Stack Overflow question, whose accepted answer suggested the use of custom CSS. I copied the CSS class name boxedmath for my blog.

Tikz to SVG in VS Code

Tue, 06 Sep 2022 23:24:28 +0200

Goal

View SVG graphics generated from TikZ code in VS Code.

Compile TikZ code and preview SVG in VS Code

with LaTeX Workship and SVG Preview

Part I: generate SVG using LaTeX Workshop

From the IDE’s parameters tab, I found the tools and recipes parameters. I clicked my user settings settings.json twice: once through the tools, and once through the recipes. Each click generated an array of default recipes or tools. Each of the former is a sequence of the later, which represents a command. The official examples and placeholders are easy to follow. Here’s the two JSON objects that I added.

Dot Products

Tue, 06 Sep 2022 11:39:46 +0200

Preface

There’s a simpler derivation using

the geometric defintion
linearity from the definition
orthogonality of the canonical basic vectors $\vec{i}$, $\vec{j}$ and $\vec{k}$.

If I had read that, I wouldn’t have type this document in LaTeX. The following content was transcribed from a PDF file that I made three days ago.

Content

Recall: $\sum_{i=m}^{n} a_{i}=a_{m}+a_{m+1}+a_{m+2}+\cdots +a_{n-1}+a_{n},$ where $m$, $n$ are integers.

Example: $\sum_{i=3}^6 i^2 = 3^2 + 4^2 + 5^2 + 6^2 = 86$

Functions for Arts

Mon, 05 Sep 2022 20:38:06 +0200

my HTML slides
You may view the source code of this blog to see the source files.

Goal

To provide an introduction to the formal definition of functions for arts stream students.

I aim to

minimize the calculations
use daily-life examples
favor pictures over text.

IT skills used

Inkscape

C-S-a for alignment.
C-S-f for boundary and colors, and line patterns (i.e. arrows).
C-S-d for document size.
clipping process:
1. prepare the object to be clipped.
2. prepare the clip, which is on top of the previous object.
3. select Object → Clip and then the first option from the top menu.

dvisvgm

Use the TEX → DVI → SVG route with latex and this tool with options --font-format=woff and -b 5 -R -d 2 to save file size and to ensure that the SVG can be correctly opened on Inkscape.

dvisvgm Guide for TikZ Pictures with Pattern Filling

Tue, 21 Jun 2022 00:31:09 +0200

Problem

I had issues in getting a SVG from a TikZ picture containing a pattern filling: https://github.com/mgieseki/dvisvgm/issues/158. The reported issue was created last year, and it’s marked as fixed. Nonetheless, I had this issue even though my MikTeX was up-to-date.

Discussion

I wanted to confirm whether my dvisvgm.exe, which had been shipped with MikTeX, was latest.
- I first asked at https://github.com/mgieseki/dvisvgm/issues/184, but I was referred to MikTeX’s GitHub repository since it’s about the MikTeX-packaged version of this tool.
- I am not sure about the technical explanation from the owner of dvisvgm at https://github.com/MiKTeX/miktex/issues/1112. It seemed that I was already using the latest stable version of this tool.
I gave a MWE illustrating the problem with the graph of y = (x + 1)² with region under the curve filled with a pattern in the above issue. I knew that’s probably off-topic, but the package owner might have some insights about the problem. It turned out that PDF → SVG was partly supported by dvisvgm. Using DVI → SVG, I managed to get the filling pattern, but I lost the beautiful Computer Modern Roman fonts—that’s another issue.
Hoping for a response from the owner for the previous problem, I started https://github.com/mgieseki/dvisvgm/issues/186. He suggested the use of --no-fonts or --font-format=woff. I observed no difference in the local filesystem. I uploaded everything I got through GitHub so that he could see what my dvisvgm.exe had output. I didn’t expected that the Computer Modern Roman fonts disappeared on GitHub side. If I hadn’t asked there, I would have never known that it’s the web browser’s security measure not to load the embedded font data in a SVG loaded from a server.

Skills learned

Meaning of some commonly used parameters of dvisvgm:

Distance From a Line

Mon, 20 Jun 2022 22:43:45 +0200

Background

A secondary school student posted a coordinate geometry question on a Discord homework help server. A helper replied to that question with an illustration of the Perpendicular Distance Formula

$$ d((x_1,y_1), L) = \frac{\lvert Ax_1 + By_1 + C \rvert}{\sqrt{A^2 + B^2}}, $$

where $L$ is the line $Ax + By + C = 0$ without proof.

Goal

To provide an illustrated derivation of this formula.

Recall

A basic property of the dot product: the “algebraic definition” is equivalent to the “geometric definition”.

Elementary Log Inequality

Sat, 18 Jun 2022 20:38:41 +0200

Goal

Show that

$$ \ln (x) \le x - 1 $$

for all $x > 0$.

Proof by inverse functions

Think about their reflection along the line $y = x$ (i.e. their inverse function). Then we get

$$e^x \ge x + 1$$

for all $x \in \Bbb{R}$, which is obviously true.

Proof by definite integrals

Here’s a second proof using definite integrals.

Case 1: x > 1

The rectangle $[1,x] \times [0,1]$ contains the region under the graph of the reciprocal $y = 1/x$ in the domain $[1,x]$.

A Plot for Euler's Constant

Fri, 17 Jun 2022 18:51:11 +0200

I firsted tried with foreach, but that would create so much paths. I found them difficult to operate on later, for example, with PGF plots library fillbetween. const plot is a better solution.

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.18}
\usetikzlibrary{patterns}
\usepgfplotslibrary{fillbetween}
\begin{document}
\newcommand\myN{8}
\pgfplotsset{
    axis lines=center,
    legend style={at={(1,1)},anchor=north east,fill=none},
    title style={at={(0.5,1.05)}},
    every axis x label/.style={
        at={(ticklabel* cs:1)},
        anchor=west,
    },
    every axis y label/.style={
        at={(ticklabel* cs:1)},
        anchor=south,
    },
}
\begin{tikzpicture}
\begin{axis}[
    title={sum of hatched region converges to Euler's constant},
    xlabel={$x$},
    ylabel={$y$},
    xmin=0,
    xmax={\the\numexpr\myN+2},
    ymin=0,
    ymax=1.3,
    xtick=\empty,
    ytick=\empty,
    extra x ticks={1, \myN},
    extra x tick labels={$1$, $n$},
    extra y ticks={1},
]
\addplot[name path=A,domain=1:\myN,samples=501,smooth] {1/x} \closedcycle;
\addlegendentry{$y = \frac{1}{x}$};
\addplot+[domain=1:\myN+1,samples=\myN+1,jump mark left,blue,mark=*,mark options={draw=blue,fill=blue}] {1/x};
\addlegendentry{$y = \frac{1}{\lfloor x \rfloor}$};
\addplot+[name path=B,domain=1:\myN+1,samples=\myN+1,jump mark left,mark=none, draw=none] {1/x} \closedcycle;
\addplot[pattern=north east lines] fill between [of=A and B];
\end{axis}
\end{tikzpicture}
\end{document}

Euler's constant illustration

SVG generated by dvisvgm

Simpler Diagram for Trigonometric Functions With Unit Circle

Wed, 15 Jun 2022 16:15:33 +0200

Background

In my previous post about unit circle and trigonometric functions, I included a graph with three trigonometry functions. I’m quite satisfied with my TikZ picture.

Problem

Unluckily, a secondary school student found that my diagram was too complicated.

Solution

\documentclass[tikz,border=2pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.18}
\usetikzlibrary{calc}
\newcommand\mytheta{110} %angle theta
\begin{document}
\begin{tikzpicture}[scale=2]
\coordinate[label=left:$O$] (O) at (0,0);
\coordinate[label=above left:${A = (\cos\theta, \sin\theta)}$] (A) at (\mytheta:1);
\coordinate[label=below left:${B = (\cos(-\theta), \sin(-\theta))}$] (B) at (-\mytheta:1);
\coordinate[label=right:$E$] (E) at (1,0);
\draw (O) circle (1);
\draw (A) -- (O)  node [midway, left] {$1$}
    -- (E);
\draw (B) -- (O);
\draw[-stealth] ($(O)!0.3!(E)$) arc (0:\mytheta:0.3) node[midway, above] {$\theta$};
\draw[-stealth] ($(O)!0.25!(E)$) arc (0:{-\mytheta}:0.25) node[midway, below] {$-\theta$};
\end{tikzpicture}
\end{document}

Tikz Illustration for Triangle Inequality

Sat, 11 Jun 2022 16:36:23 +0200

I thought the code would be easy, but it turned out that I spent one hour and half to draw this figure.

\documentclass[border=2pt,preview]{standalone}
\usepackage{tikz}
\usepackage{caption}
\newcommand{\sideA}{2}
\newcommand{\sideB}{3}
\newcommand{\sideC}{6}
\colorlet{myred}{red!40!yellow}
\colorlet{mygreen}{green!40}
\colorlet{myblue}{blue!20}
\begin{document}
\begin{figure}
\centering
\begin{tikzpicture}[thick]
\coordinate (A) at (0,0);
\coordinate (B) at (\sideC,0);
\draw[<->,>=stealth,myred] (A) -- ++ (-\sideA, 0) node [pos=0.5,below] {$\color{myred}{a}$};
\draw[<->,>=stealth,mygreen] (B) -- ++ (\sideB, 0) node [pos=0.5,below] {$\color{mygreen}{b}$};
\draw[<->,>=stealth,myblue] (A) --  (B) node [pos = 0.5, below]{$\color{myblue}{c}$};
\draw[dashed,myred] (A) circle (\sideA);
\draw[dashed,mygreen] (B) circle (\sideB);
\end{tikzpicture}
\captionsetup{labelformat=empty}
\caption{triangle inequality ${\color{myred}{a}} + {\color{mygreen}{b}} >
  {\color{myblue}{c}}$ with $\color{myred}{a = \sideA}$,
  $\color{mygreen}{b = \sideB}$, $\color{myblue}{c = \sideC}$}
\end{figure}
\end{document}

The colors are customized for the Discord bot TeXit.

Git Warning: LF Will Be Replaced by CRLF

Fri, 10 Jun 2022 20:18:01 +0200

I’m using Git Bash while writing this post. I’ve never tested the commands on *nix.

Background

Some of the tags and titles were written as “LateX”/“latex” in the source files. I batch corrected them with Git Grep and GNU Sed.

git grep --name-only -IiE ^-\ latex$'\r'? content/{post,page} | \
xargs -n1 sed -i "s/^- latex/- LaTeX/I"

I tried to match

a leading - using ^-
a whitespace \ escaped by a backslash to avoid wrapping the special character below with double quotes
the string “latex” (case-insensitive)
the carriage return \r, which is represented by $'\r' in bash, for at most once (?)

I observed that wrapping $'\r' with "" would lead to no match.

LaTeX Table Background Color for TeXit

Fri, 10 Jun 2022 11:54:47 +0200

Problem

In my previous post about LaTeX tables, I used \cellcolor{white} to override the \rowcolor{cyan} in a cell in the leftmost column, which was the column type name.

On Discord, that cell became black because TeXit inverted black and white.

Discussion

I first tried blending black and white, and I found that black!27 and black!28 give a good approximation to Discord’s background color.

Thanks to this Discord Color Palette and a bot command channel on a server, I’ve observed that the desired color is RGB(54,57,62).

Line Equation in Intercept Form

Thu, 09 Jun 2022 09:26:54 +0200

This is a first draft of a TikZ picture illustraing this classical formula to be used for math help channels.

Adding \caption{for the picture} without “Figure 1:” requires \usepackage{caption} and wrapping with \begin{figure}. It also possible to use the primitive TeX command \par, but it would be complicated to use that with standalone. In the previous post, the SVG picture from the LaTeX table in an article has too much useless whitespace around the table. I don’t bother to learn other packages, as I need time for other more important stuff.

LaTeX Multirow Multicol Table Coloring

Thu, 09 Jun 2022 00:45:55 +0200

Inspiration

Number of two-digit numbers not containing the digit ‘8’.

Code

The standalone class can’t be used with \caption.
*{8}{c} means 8 c.
>{\columncolor{cyan}}c gives the column color. It \usepackage[table]{xcolor}.
\rowcolor{cyan} overrides the column colors.
\cellcolor{white} overrides the above two commands. It has to be carried out one-by-one without any fancy package.
\multicolumn{n}{<alignment>}{content} defines a multi-column cell.
\multirow{n}{*}{content} defines a multi-row cell. It \usepackage{multirow}. It can’t contain \multicolumn.
\cline{i-j} draws a horizontal line above the row from column i to column j.
No fancy way of coloring multirow cells without fancy packages.
\multirow{-9} at the last row creates a cell spanning nine rows from bottom to above, so that its content won’t be covered by colors of former rows.
\rotatebox[origin=[clr]]{angle}{content}: rotate content by angle anticlockwise with [clr] as the rotation center.

\documentclass[12pt]{article}
\usepackage{multirow}
\usepackage[table]{xcolor}
\usepackage{tikz}
\begin{document}
\begin{table}[htbp]
\centering
\caption{Sample \LaTeX{} multirow table}
\vspace*{1ex}
\label{multiprogram}
\begin{tabular}{|c|c|*{8}{c}>{\columncolor{cyan}}cc|}
\hline
\multicolumn{2}{|c|}{\multirow{2}{*}{}} & \multicolumn{10}{c|}{unit digit} \\\cline{3-12}
\multicolumn{2}{|c|}{} & 0 & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 \\\hline
& 1 & &  &  &  &  &  &  &  &  &  \\
& 2 & &  &  &  &  &  &  &  &  &  \\
& 3 & &  &  &  &  &  &  &  &  &  \\
& 4 & &  &  &  &  &  &  &  &  &  \\
& 5 & &  &  &  &  &  &  &  &  &  \\
& 6 & &  &  &  &  &  &  &  &  &  \\
& 7 & &  &  &  &  &  &  &  &  &  \\
\rowcolor{cyan} \cellcolor{white}
& 8 & &  &  &  &  &  &  &  &  &  \\
\multirow{-9}{*}{\rotatebox[origin=c]{90}{tens digit}}
& 9 & &  &  &  &  &  &  &  &  &  \\\hline
\end{tabular}
\end{table}
\end{document}

Result:

Upgrade Font Awesome in Beautiful Hugo Theme

Tue, 07 Jun 2022 13:02:33 +0200

Background

Beautiful Hugo comes with Font Awesome icons. However, it seems that it’s no longer maintained.

Goal

To upgrade Font Awesome to the current stable version (6.1.1).

Problem

The official guide for self-hosting Font Awesome Web Fonts + CSS suggests users to place the following files

filepath	role
`/fontawesome/webfonts/`	Free Web Fonts
`/fontawesome/css/all.min.css`	CSS file for using Free Web Fonts

into somewhere in my theme. The left column of the diagram features the folder assets/.

Second Homothety between Nine-Point Circle and Circumcircle

Mon, 06 Jun 2022 04:36:17 +0200

Motivation

I saw someone illustrating his/her solution with a “superior triangle”.

This reminds me the homothety about the centroid of factor −1/2.

The above picture \usetikzlibrary{calc} for computing coordinates from those of existing points. (A)!.25!(B) means $(A)+.25[(B)-(A)]$ .

\begin{tikzpicture}[scale=2]
\coordinate (D) at (-0.7,1);
\coordinate (E) at (-1,0);
\coordinate (F) at (1,0);
\coordinate (A) at ($(E)!.5!(F)$);
\coordinate (B) at ($(F)!.5!(D)$);
\coordinate (C) at ($(D)!.5!(E)$);
\coordinate (G) at ($(D)!.5!(E)!1/3!(F)$);

\draw (A) -- (B) -- (C) -- cycle;
\draw (D) -- (E) -- (F) -- cycle;
\begin{scriptsize}
\fill (G) circle (0.5pt) node [left=2pt,anchor=north]{$G$};
\end{scriptsize}
\draw[->,-latex,dashed] (D) -- (A);
\draw[->,-latex,dashed] (E) -- (B);
\draw[->,-latex,dashed] (F) -- (C);
\end{tikzpicture}

From the homothety between the nine-point circle and circumcircle about orthocenter with a factor of 2, we see that the nine-point center is the mid-point of orthocenter and circumcenter.

Basic Symmetries in Nine-Point Circle

Sat, 04 Jun 2022 22:29:26 +0200

Motivation

Someone on Discord asked about the existence of the nine-point circle. It’s well-known that that can be proved by homothety.

Little reminder about homothety

Homothety preserves angles (and thus parallel lines). Homothetic polygons are similar, so the ratio of the corresponding sides is the same. Considering the radii of a circle under a homothety, we see that a homothety maps a circle to another circle.

Notation

H: orthocenter
G: centroid
O: circumcenter
ω: circumcircle
H_A: feet of altitude with respect to A.
M_A: midpoint of side a.
E_A: Euler point with respect to A. (i.e. midpoint of A and H)

Problem

The second proof for nine-point circle on AoPS starts with a proved fact that the reflection of H about a and M_A lie on ω.

Dvisvgm's Issue With Fill Pattern

Sat, 04 Jun 2022 20:56:57 +0200

Goal

Generate SVG file for TikZ graphics.

Method

TeX → PDF with PDFLaTeX
PDF → SVG with dvisvgm -P filename

Example: I generated a PGF plot from the source code on my personal template.

Problem

When I applied this method to the following TeX code in my previous post, dvisvgm -P returns a blank SVG.

\documentclass[tikz,border=2pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.6}
\usetikzlibrary{patterns}
\begin{document}
\begin{tikzpicture}
\begin{axis}[axis lines=center,legend style={at={(0.7,0.7)},anchor=south west}]
\addplot [domain=-3:3, thick, smooth, yellow] { 1/sqrt(2*pi)*exp(-x^2/2) };
\addlegendentry{$y = \frac{1}{\sqrt{2\pi}} e^{-x^2/2}$};
\addplot [dashed, yellow] coordinates {(1.5,0) (1.5,0.14)};
\addlegendentry{99th percentile};
\addplot[domain=-3:1.5, pattern=north east lines,draw=none, fill opacity=0.3]
  { 1/sqrt(2*pi)*exp(-x^2/2) } \closedcycle;
\end{axis}
\end{tikzpicture}
\end{document}

This code passes the compiler.

To Be Improved Normal Curve

Sat, 04 Jun 2022 13:27:33 +0200

Adaptations for standalone documents:

\usetikzlibrary{pattern} before \begin{document}
\pgfplotsset{compat=1.6}

\begin{tikzpicture}
\begin{axis} [axis lines=center,legend style={at={(0.7,0.7)},anchor=south west}]
\addplot [domain=-3:3, thick, smooth, yellow] { 1/sqrt(2*pi)*exp(-x^2/2) };
\addlegendentry{$y = \tfrac{1}{\sqrt{2\pi}} e^{-x^2/2}$};
\addplot [dashed, yellow] coordinates {(1.5,0) (1.5,0.14)};
\addlegendentry{99th percentile};
\addplot[domain=-3:1.5, pattern=north east lines,draw=none, fill opacity=0.3]
{ 1/sqrt(2*pi)*exp(-x^2/2) } \closedcycle;
\end{axis}
\end{tikzpicture}

Trigonometric Functions by Unit Circle

Fri, 03 Jun 2022 11:21:20 +0200

For secondary school students, I define cosine and sine as the x and y-components of the point A (cos θ, sin θ) on the unit circle x² + y² = 1, and the tangent function as the quotient of sine over cosine.

\begin{tikzpicture}[scale=3]
\coordinate (O) at (0,0);
\coordinate (H) at (0.6,0);
\coordinate (A) at (0.6,0.8);
\coordinate (E) at (1,0);
\coordinate (T) at (1,0.8/0.6);
\draw (O) circle (1);
\draw[->] (-1.3,0) -- (1.3,0) node [right]{$x$};
\draw[->] (0,-1.3) -- (0,1.3) node [above]{$y$};
\begin{scope}[thick]
\draw (O) node [below left] {$O$}
    -- (H) node [below right] {$H$}
    node [below, midway] {$\cos \theta$}
    -- (A) node [below, midway, sloped] {$\sin \theta$}
    node [above=5pt] {$A$}
    -- cycle node [above left, midway] {$1$};
\begin{scope}
    \clip (O) -- (A) -- (H) -- cycle;
    \draw (O) circle (0.1) node[right=7pt, above=5pt, anchor=west] {\small $\theta$};
\end{scope}
\draw (H) rectangle ++(-0.1,0.1);
\draw (E) rectangle ++(-0.1,0.1);
\draw (E) node [below right] {$E$}
    -- (T) node [below, midway, sloped] {$\tan \theta$}
    node [above, right] {$T$}
    -- (A);
\end{scope}
\end{tikzpicture}

Matrix Diagonalisation and Change of Basis

Thu, 02 Jun 2022 14:24:19 +0200

Here’s the $\LaTeX$ code of my diagram for matrix diagonalisation to be used on Discord.

Why do matrix diagonalisation on square matrix $P$?

If we can find a diagonal matrix $D$ and a square matrix $Q$ such that $P = QDQ^{-1}$, then we can easily compute $(P + \lambda I)^n$ for any scalar $\lambda$ and integer $n$ because $D^n$ is easy to compute.

\[\begin{tikzcd}
    {{}} & {{}} & \cdots & {} \\
    {{}} & {{}} & \cdots & {{}}
    \arrow["P", from=1-1, to=1-2]
    \arrow["{Q^{-1}}"', from=1-1, to=2-1]
    \arrow["D"', from=2-1, to=2-2]
    \arrow["Q"', from=2-2, to=1-2]
    \arrow["P", from=1-2, to=1-3]
    \arrow["D"', from=2-2, to=2-3]
    \arrow["P", from=1-3, to=1-4]
    \arrow["D"', from=2-3, to=2-4]
    \arrow["Q"', from=2-4, to=1-4]
\end{tikzcd}\]

After viewing the power of the Discord bot $\TeX{}$it, which renders $\LaTeX$ code on Discord, I gave up spending more time on exploring more functionalities of $\KaTeX$ (say, commutative diagrams) because Discord and $\LaTeX$ spread math knowledge much better than a static blog for basic math: the former allows instant feedback from the reader. The later is better for taking notes. To display more complicated graphics, I can compile to PDF first, then use dvisvgm with -P for --pdf. (The small -p selects --page=ranges.)

LaTeX Code for Linear System

Wed, 01 Jun 2022 16:25:10 +0200

\begin{align} A\mathbf{x} &= \mathbf{b} \\ \begin{pmatrix} a_{11} & a_{12} & a_{13} \\ a_{21} & a_{22} & a_{23} \\ a_{31} & a_{32} & a_{33} \end{pmatrix} \begin{pmatrix} x_1 \\ x_2 \\ x_3 \end{pmatrix} &= \begin{pmatrix} b_1 \\ b_2 \\ b_3 \end{pmatrix} \\ \begin{bmatrix} \vert & \vert & \vert \\ \mathbf{a}_1 & \mathbf{a}_2 & \mathbf{a}_3 \\ \vert & \vert & \vert \end{bmatrix} \begin{bmatrix} x_1 \\ x_2 \\ x_3 \end{bmatrix} &= \mathbf{b} \\ x_1 \mathbf{a}_1 + x_2 \mathbf{a}_2 + x_3 \mathbf{a}_3 &= \mathbf{b} \tag{$\star$} \\ \begin{pmatrix} a_{11} x_1 + a_{12} x_2 + a_{13} x_3 \\ a_{21} x_1 + a_{22} x_2 + a_{23} x_3 \\ a_{31} x_1 + a_{32} x_2 + a_{33} x_3 \end{pmatrix} &= \begin{pmatrix} b_1 \\ b_2 \\ b_3 \end{pmatrix} \\ x_1 \begin{pmatrix} a_{11} \\ a_{21} \\ a_{31} \end{pmatrix} + x_2 \begin{pmatrix} a_{12} \\ a_{22} \\ a_{32} \end{pmatrix} + x_3 \begin{pmatrix} a_{13} \\ a_{32} \\ a_{33} \end{pmatrix} &= \begin{pmatrix} b_1 \\ b_2 \\ b_3 \end{pmatrix} \end{align}

Source code:

Tikz Templates

Mon, 23 May 2022 14:12:18 +0200

Load TikZ in either one way.

\documentclass[tikz, border=2pt]{standalone}
\usepackage{tikz}

Graph

With pgfplots

PGF Plots automizes the axes configurations, for example:

major and minor ticks and labels on the axes
major and minor grid lines
legend styles and positioning

Simplest example for Discord:

\begin{tikzpicture}[declare function={f(\x)=(\x)^2/2 - 5;}]
\begin{axis}[
  axis equal,
  grid=both,
  grid style={line width=.2pt, draw=gray},
  minor tick num=1,
  xtick={-4,-2,...,4},
  ytick={-4,-2,...,4},
  axis lines=center,
  title={Graph of $y = \frac12 x^2 - 5$},
]
\addplot[yellow,domain=-4:4] {f(\x)};
\pgfplotsset{
  grid style={gray},
  major grid style={gray,line width=0.7}
}
\end{axis}
\end{tikzpicture}

TeXit’s output:

Polar Rose in Julia

Wed, 25 Aug 2021 17:00:56 +0200

Background

I’m doing exercise 4.9 of Think Julia, which asks for a function for a polar rose using Luxor’s turtle graphics.

Difficulties

Work out the geometric structure of the family of polar roses. The key is to construct some auxiliary isoceles triangles and work out the angles between them. One sees that they are parametrized by two varaibles n and k.
- n: number of petals
- k: petal increment
- constraint: k ≠ n ÷ 2
Handle the case when gcd(n, k) > 1, i.e. more than one closed loop.
The positive x direction goes to the right; the positive y direction goes down.

Attempt

Use ThinkJulia.Reposition(t::Turtle, x, y) to reposition the turtle.
Use turn(t::Turtle, θ) to turn t
Use ThinkJulia.Orientation(t::Turtle, θ) to restore the turtle’s orientation after the move.

Code

I spend three days writing and testing this function.

Deploy Hugo Theme exampleSite With Github Actions

Sat, 06 Mar 2021 13:39:05 +0100

Motivation

To test PRs on the upstream of a Hugo theme by setting up a testing branch.

Goal

To deploy a forked GitHub repo for a Hugo theme with exampleSite to GitHub Pages using GitHub Actions.

The whole article is based on my fork of Hugo Future Imperfect Slim.

References

Difficulties

I had failed for about ten times before I got the job done.

First Experience with ASP.NET Core MVC & PostgreSQL

Mon, 01 Mar 2021 17:29:50 +0100

Goal

To build an ASP.NET Core 5 MVC web app linked with a PostgreSQL.

Motivation

SQL Server is proprietary.
SQLite used in Microsoft’s ASP.NET Core 5 MVC tutorial isn’t made for web apps.
MySQL doesn’t perform well with concurrent read-writes. It’s dual-licensed like GitLab.
Some users find PostgreSQL cost-effective.

Useful tutorials

MS’s tutorial in item 2 above.
Wes Doyle’s YouTube video goes through the steps
MS’s tutorial for Razor Pages with EF Core migrations

Steps

Create a superuser in the database.

Deleted Question on Semi-Simple and Projective but not Injective Module

Thu, 14 Jan 2021 10:39:00 +0100

A backup of a deleted PSQ : https://math.stackexchange.com/q/3955443/290189

OP : irfanmat

It has a detailed answer by Atticus Stonestrom. It’s pity that his post got deleted. As there’s no reason for undeletion, I’m posting it here so as to preserve the contents.

Question body

Is there a semi-simple and projective but not injective module? I will be glad if you help.

Response(s)

In the non-commutative case, the answer is yes. Consider $R$ the ring of upper triangular $2\times 2$ matrices over a field $F$, and denote by $e_{ij}$ the element of $R$ with the $ij$-th entry equal to $1$ and all other entries equal to $0$. We can decompose $R$ as a direct sum of left ideals $$Re_{11}\oplus (Re_{12}+Re_{22})=Re_{11}\oplus Re_{22},$$ so let $M=Re_{11}$. Then $M$ is clearly simple, and – as a direct summand of the free module $R$ – is also projective. However, $M$ is not injective; consider the map $f:Re_{11}\oplus Re_{12}\to M$ taking $e_{11}$ and $e_{12}$ to $e_{11}$. $Re_{11}\oplus Re_{12}$ is a left ideal of $R$, but there is no way to extend $f$ to a map $R\rightarrow M$, so this gives the desired example.

Another Math.SE Double Integral Using Polar Coordinate

Sun, 10 Jan 2021 16:40:17 +0100

I wanted to post the following answer to a question on double integral on Math.SE, but someone had submitted his work before I finished typing. As a result, I’m posting this on my personal blog.

Let $r = \sqrt{x^2+4y^2}$ and $t = \begin{cases} \tan^{-1}(2y/x) &\text{ if } x > 0 \\ \pi/2 &\text{ if } x = 0. \end{cases}$ Then $\begin{cases} x &= r \cos t \\ y &= (r \sin t)/2 \end{cases}$ and $D = { (r,t) \mid r \ge 0, t \in [\pi/4, \pi/2] }$. Calculate the Jacobian

Ways to Draw Diagrams Displayed on Math.SE

Wed, 23 Dec 2020 11:46:47 +0100

I wanted to start a meta question, but I don’t see a point of that after viewing some related posts listed at the end of the next subsection.

Intended question

You may vote on your preferred way.

Ways	Advantages	Disadvantages
AMScd	supported on Math.SE for a long time	no diagonal arrows syntax less well-known Two-way arrows $\rightleftarrows$ look odd
`array`	supported on Math.SE for a long time easier syntax write basic diagonal arrows like $\nearrow$	fine tuning spacing is hard diagonal arrows only work for neighboring nodes
ASCIIFlow	WYSIWYG interface	lines are rendered as slashes in code
TikZ	well known syntax can draw pretty diagrams	not supported on SE, need to import as picture
others?

Combat Procrastination

Mon, 23 Nov 2020 09:06:04 +0100

My notes for a YouTube video about procrastination on one hearing only.

Why?

Boring tasks.

It’s necessary?
- Yes: Make it fun.
  - Get a study partner.
  - Find a more energetic time.
- No: Get rid of it.
Surrounding environment.
- Identify someone who procrastinates in your circle of influence.
- Distance yourself from them, or
- Be aware of what their behavior.
Perfectionism
- Know about yourself.
- Reality: nothing can be perfect.

Five strategies against procrastination:

Decompose a huge task into smaller parts.

GIMP w'ont Start after Ubuntu Distro Upgrade

Fri, 09 Oct 2020 17:04:18 +0200

Problem

After upgrading to Ubuntu 20.04 form 18.04, I wasn’t able to start GIMP 2.10. The message was in the same format as that in a related Ask Ubuntu question, except that the version numbers were greater.

I attempted installing the package gegl, which was irrelavant to the problem.

Analysis

I found the answers mentioning the package libgegl helpful.

$ dpkg -l | grep gegl
ii  gegl                                       0.4.22-3                         
     amd64        Generic Graphics Library Test Program
ii  libgegl-0.4-0:amd64                        1:0.4.18+om-0ubu18.04.18~ppa     
     amd64        Generic Graphics Library
ii  libgegl-common                             1:0.4.18+om-0ubu18.04.18~ppa     
     all          Generic Graphics Library - common files

Despite deletion of ppa:otto-kesselgulasch/gimp by ppa-purge, that leaves a trace in /etc/apt/sources.list.d.

Recover Mysql Root Password

Wed, 07 Oct 2020 13:13:08 +0200

Just a little linklog to a relevant page on How to Forge. Root privileges are needed.

Stop service: service mysql stop
Start MySQL server w/o password: mysqld_safe --skip-grant-tables &
Connect to CLI client as root: mysql -u root

Reset root password. Here’s the syntax for ≥v.5.7.6.

mysql> use mysql;
mysql> SET PASSWORD FOR 'root'@'localhost' = PASSWORD("newpass");
mysql> flush privileges;
mysql> quit

Repeat step 1, or killall mysqld if it doesn’t work. Output can be different on different Linux distro.

Pandoc LaTeX Mermaid on GitLab CI

Fri, 28 Aug 2020 09:26:29 +0200

Goal

To provide an open-source alternative to the Docker image escalope/pandoc-mermaid-plantuml, whose Dockerfile isn’t available.

The rationale behind these difficult setup is simple: construct informative Mermaid diagram with intuitive Markdown syntax in an open-source and economic way.

This newly constructed Docker image is entirely on GitLab. No Docker Hub account is needed. For sample usage, consult .gitlab-ci.yml in my test project.

Difficulties

issues raghur/mermaid-filter#51 and #52
issue gitlab-org/gitlab-runner#4566

Useful code/articles

time-machine-project/requests-for-comments@470b0c5 Dockerfile
Reduce Docker Image Sizes Using Alpine
Best practices for building docker images with GitLab CI with the accompanying gist
The code block in the highlighted comment in item 2 of the above section
pandoc installation for Docker
Sample Dockerfile for Alpine Linux in the troubleshooting of Puppeteer
sc250024/docker-mermaid-cli@3c9ddb5 src/puppeteerConfigFile.json
raghur/mermaid-filter project README’s section about Puppeteer config file

Site Maintenance for Hugo v0.60

Tue, 14 Apr 2020 16:33:31 +0200

Background

I lacked motivation to keep this tweaked theme up with Hugo’s development after last summer. When I came back yesterday, I saw that some pages using Font Awesome icons were broken. Apart from that, the ToC list level problem resurfaced.

Fixed ToC

The solution that I had adopted no longer worked. Luckily, some users provided a shorter code in the later discussions. The one from user501254 caught me. I first tried to copy his code into the partial layout for ToC. However, nothing changed.

Set up GitHub Actions for Beautiful Jekyll

Mon, 02 Sep 2019 23:23:25 +0200

GitHub Actions provide CI/CD support, which might interest many GitHub users. I’ve applied for this feature a week ago. Luckily, my application for the trial was approved by GitHub. Tonight, I’ve found the motivation for making my first step in my forked repo VincentTam/beautiful-jekyll.

My setup:

Clicked on the “Action” tab of the repo.
Chose the workflow file template for Jekyll.
Added a slash / in front of srv in chmod 777 srv/jekyll, so as to fix the “no such file or directory” error.
Added the parameter repository: {your repo name} in the site config file _config.yml.

The action should be successfully configured.

Customized Archetype for This Site

Sat, 10 Aug 2019 16:28:46 +0200

Background

I prefer including the date into the Permalink of a post. Everytime I create a new post, I type

hugo new post/$(date -I)-post-title.md

to ensure that the date is correct.

Problem

The title field in the post’s front matter contained the date, which wasn’t something that I wanted because it’s already shown next to the icon.

Observations

Neither \d nor [\d] works for the PCRE character class \d.

Icon in Hugo Navbar

Sat, 10 Aug 2019 14:53:00 +0200

Motivation

The original navbar in words took up half of the horizontal spaces of the viewport. I couldn’t add new items like “Tags” to display the tag list.

Work

Thanks to the pre field in Hugo Menus, one can easily add the icon as an HTML element by some editing on the template file.

{{ range .Site.Menus.main.ByWeight }}
  {{ if .HasChildren }}
    <li class="navlinks-container">
      {{ if .Pre }}
        <a class="navlinks-parent" title="{{ .Name }}">{{ .Pre }}</a>
      {{ else }}
        <a class="navlinks-parent">{{ .Name }}</a>
      {{ end }}
      <div class="navlinks-children">
        {{ range .Children }}
          {{ if .Pre }}
            <a title="{{ .Name }}" href="{{ .URL | relLangURL }}">{{ .Pre }}</a>
          {{ else }}
            <a href="{{ .URL  | relLangURL }}">{{ .Name }}</a>
          {{ end }}
        {{ end }}
      </div>
    </li>
  {{ else }}
    <li>
      {{ if .Pre }}
        <a title="{{ .Name }}" href="{{ .URL | relLangURL }}">{{ .Pre }}</a>
      {{ else }}
        <a href="{{ .URL | relLangURL }}">{{ .Name }}</a>
      {{ end }}
    </li>
  {{ end }}
{{ end }}

Network Interface Name Detection in Conky

Thu, 08 Aug 2019 18:42:08 +0200

When one changes connection type (say, from ethernet to Wi-Fi), the interface name changes (e.g. eth0 → wlan1). To avoid changing Conky config file all the time, here’s a little Lua function for finding the network interface name.

function findInterface()
    local handle = io.popen('ip a | grep "state UP" | cut -d: -f2 | tr -d " "')
    local result = handle:read('*a'):gsub('\n$','')
    handle:close()
    return result
end

ip a gives everything about connection info. Each entry looks like

 3: wlp3s0f0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000

Grep the “state UP” and extract the second field, using : as a delimiter. Trim off the spaces around.

Staticman Script in Pure JS

Mon, 05 Aug 2019 09:56:16 +0200

The official Staticman script sample depends on jQuery. I have been using jQuery in my Staticman script for nested comments for more than six months.

Recently, in the new release of Hugo Swift Theme, in which I’m a collaborator, one has removed all jQuery methods at commit f137efa4. Here’s the structure of the script:

auxiliary functions like elem, elems, pushClass, deleteClass, etc.
A self-executing function comments()
- some necessary local variables
- handleForm() consisting merely of an event listener handling form submission.
  - formToJSON(form) for converting the comment form to a JSON string.
  - fetch(url, {...}).then(...).catch(...) for submitting a sever request and handling its response. It calls showModal(...) and it contains resetForm().
- a conditional form ? handleForm(form) : false; to execute the above method provided the existence of the comment form.
- closeModal() and showModal() for closing and showing the modal respectively.
- a conditional containsClass(body, show) ? closeModal() : false;.
- a self-executing toogleForm() function. Nesting a self-executing function inside another one limits the namespace of variables. Even though there’s no new variable defined inside this function, there’s a need to wrap it with parenthesis () because toggleForm() is not called elsewhere, unlike toggleMenu(). If the if(button){...} statement comes out directly, we will not know that it’s doing.

Staticman With Introduction Theme

Fri, 02 Aug 2019 19:01:07 +0200

Goal

To port Huginn’s Staticman integration to Introduction.

Difficulties

I’ve used some class names from Minimal Mistakes since the modals in the original code clashes with Introduction’s mobile responsive card display for projects. If I had know the practice of prepending a CSS class to avoid overiding the CSS properties of other components of a web site, I wouldn’t have mixed this Jekyll theme with my template for nested comments.

Due to my existing work on my SASS file for Staticman + Introduction, I had decided to continue working with the class names in this SASS file. Changing the CSS class names in the JS script was easier than doing so in the SASS file since I was more familiar with the former.

CPU Temperature Display in Conky

Wed, 31 Jul 2019 15:04:59 +0200

Background

I’m using Conky for monitoring the system. After a system upgrade, the CPU temperatures were gone. Conky’s standard error showed the following.

Conky: can't open '/sys/class/hwmon/hwmon0/temp3_input': No such file or
directory please check your device or remove this var from Conky...

Source of message: https://bbs.archlinux.org/viewtopic.php?id=82231

An easy fix would be to adjust the following lines in .conkyrc according to the number N in /sys/class/hwmon/hwmonN containing the file temp3_input. (You may adjust the number 3 according to the number of CPU of your device.) The number of CPU can be found using grep -c ^processor /proc/cpuinfo.

Animated GIF Screenshots on Ubuntu

Wed, 31 Jul 2019 12:56:31 +0200

Background

I’ve to take screenshots to demonstrate Conky’s visual output.

I’ve chosen Byzanz after reading this answer on Ask Ubuntu.

Peek is more user-friendly, but I prefer CLI’s precision. That’s feasible thanks to a comment mentioning xwininfo.

After typing xwininfo, click on the target window. Switching to adjacent workplace is possible.

$ xwininfo
xwininfo: Please select the window about which you
          would like information by clicking the
          mouse in that window.

xwininfo: Window id: 0x1c0000a "Desktop"

  Absolute upper-left X:  0
  Absolute upper-left Y:  0
  Relative upper-left X:  0
  Relative upper-left Y:  0
  Width: 1920
  Height: 1080
  Depth: 32
  Visual: 0x1a7
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x1c00009 (not installed)
  Bit Gravity State: NorthWestGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: no
  Map State: IsViewable
  Override Redirect State: no
  Corners:  +0+0  -0+0  -0-0  +0-0
  -geometry 1920x1080+0+0

The --x and --y parameters below correspond to the absolute upper-left position of the window.

More Static Nested Comments

Tue, 30 Jul 2019 21:05:35 +0200

Background

I’ve made nested comment support for Beautiful Hugo, which I’ve ported to other Hugo themes like Introduction, Hyde-hyde, etc.

Problem I

Some of those Hugo themes that I worked with did show the HTML form, but the CSS styles were gone on the GitLab Pages.

Reason I

This is due to the lack of resources/_gen/ in the indexed repo for themes making use of assets/.

Solution I

Check that you have the required prerequisites. For example, Introduction requires autoprefixer and postcss-cli.
Update submodule for the theme in the directory holding the source code of the static site.
Type hugo [server] so that the resources are locally generated.
Push the repo.

Problem II

The approach in my linked blog post is too complicated. It makes use of a mix of JavaScript and Hugo template. This can be hard to comprehend and port, since the file structure for JavaScripts isn’t the same in different themes. It’s better to make the internal referencing for nested comment display entirely in Hugo.

Huginn Theme With Staticman

Sun, 19 May 2019 19:26:28 +0200

Goal

To provide Staticman support to the Hugo theme Huginn.

Motivation

A Framagit user tried using the public GitLab instance but failed. Finally, he removed Staticman from his site and his Hugo theme.

If I had been notified, I would have explained that that was due to the constraint of gitlabBaseUrl, which could only take one GitLab instance.

In response to demand for Staticman from Framagit users, I set up another GitLab instance of Staticman API and forked some Hugo/Jekyll repo under the project page Staticman et GitLab Pages.

Right PATH to Linux

Sat, 18 May 2019 11:25:57 +0200

Background

Updated $\LaTeX$ version

From this $\TeX$-SE question about tlmgr, we see some advantages of installing $\TeX$Live directly from the official site:

avoid errors due to outdated version of $\TeX$Live supplied by the OS’s package manager
easier to manage packages with tlmgr.
enjoy the newer version of $\TeX$Live not yet available in your current GNU/Linux version.

The installation took about 30 minutes and 5G in the disk. I’ve chosen a local installation as this didn’t require sudo privileges. The whole process went smooth and the system displayed a message about setting

Package Versioning for Julia Projects

Thu, 09 May 2019 13:32:11 +0200

Update: Thanks to JuliaRegistries/General#647, the version cap of the package Distributions has now been removed, so that one can directly install the package GLM along with Distributions v0.19.2.

Background

I’m reading the book Statistics with Julia, which makes use of GLM.

Problem

I encountered the following error, which I posted in the issue GLM.jl#311.

(v1.1) pkg> add GLM
 Resolving package versions...
ERROR: Unsatisfiable requirements detected for package GLM [38e38edf]:
 GLM [38e38edf] log:
 ├─possible versions are: [0.2.0-0.2.5, 0.3.0-0.3.2, 0.4.0-0.4.8, 0.5.0-0.5.6, 0
.6.0-0.6.1, 0.7.0, 0.8.0-0.8.1, 0.9.0, 0.10.0-0.10.1, 0.11.0, 1.0.0-1.0.2, 1.1.0
-1.1.1] or uninstalled
 ├─restricted to versions * by an explicit requirement, leaving only versions [0
.2.0-0.2.5, 0.3.0-0.3.2, 0.4.0-0.4.8, 0.5.0-0.5.6, 0.6.0-0.6.1, 0.7.0, 0.8.0-0.8
.1, 0.9.0, 0.10.0-0.10.1, 0.11.0, 1.0.0-1.0.2, 1.1.0-1.1.1]
 ├─restricted by compatibility requirements with DataFrames [a93c6f00] to versio
ns: [0.4.0-0.4.8, 0.5.0-0.5.6, 0.6.0-0.6.1, 0.7.0, 0.8.0-0.8.1, 0.9.0, 0.10.0-0.
10.1, 0.11.0, 1.0.0-1.0.2, 1.1.0-1.1.1] or uninstalled, leaving only versions: [
0.4.0-0.4.8, 0.5.0-0.5.6, 0.6.0-0.6.1, 0.7.0, 0.8.0-0.8.1, 0.9.0, 0.10.0-0.10.1,
 0.11.0, 1.0.0-1.0.2, 1.1.0-1.1.1]
 │ └─DataFrames [a93c6f00] log:
 │   ├─possible versions are: [0.1.0, 0.2.0-0.2.5, 0.3.0-0.3.16, 0.4.0-0.4.3, 0.
5.0-0.5.12, 0.6.0-0.6.11, 0.7.0-0.7.8, 0.8.0-0.8.5, 0.9.0-0.9.1, 0.10.0-0.10.1, 
0.11.0-0.11.7, 0.12.0, 0.13.0-0.13.1, 0.14.0-0.14.1, 0.15.0-0.15.2, 0.16.0, 0.17
.0-0.17.1, 0.18.0-0.18.2] or uninstalled
 │   └─restricted to versions 0.18.2 by an explicit requirement, leaving only ve
rsions 0.18.2
 ├─restricted by compatibility requirements with StatsBase [2913bbd2] to version
s: [0.11.0, 1.0.0-1.0.2, 1.1.0-1.1.1] or uninstalled, leaving only versions: [0.
11.0, 1.0.0-1.0.2, 1.1.0-1.1.1]
 │ └─StatsBase [2913bbd2] log:
 │   ├─possible versions are: [0.1.0, 0.2.0-0.2.1, 0.2.3-0.2.10, 0.3.0-0.3.13, 0
.4.0-0.4.4, 0.5.0-0.5.3, 0.6.0-0.6.16, 0.7.0-0.7.4, 0.8.0-0.8.3, 0.9.0, 0.10.0, 
0.11.0-0.11.1, 0.12.0, 0.13.0-0.13.1, 0.14.0-0.14.1, 0.15.0, 0.16.0-0.16.1, 0.17
.0, 0.18.0, 0.19.0-0.19.5, 0.20.0-0.20.1, 0.22.0, 0.23.0-0.23.1, 0.24.0, 0.25.0,
 0.26.0, 0.27.0, 0.28.0-0.28.1, 0.29.0, 0.30.0] or uninstalled
 │   └─restricted to versions 0.30.0 by an explicit requirement, leaving only ve
rsions 0.30.0
 └─restricted by compatibility requirements with Distributions [31c24e10] to ver
sions: uninstalled — no versions left
   └─Distributions [31c24e10] log:
     ├─possible versions are: [0.1.0-0.1.4, 0.2.0-0.2.13, 0.3.0, 0.6.4-0.6.7, 0.
7.0-0.7.6, 0.8.0-0.8.10, 0.9.0, 0.10.0-0.10.2, 0.11.0-0.11.1, 0.12.0-0.12.5, 0.1
3.0, 0.14.0-0.14.2, 0.15.0, 0.16.0-0.16.4, 0.17.0, 0.18.0, 0.19.1-0.19.2] or uni
nstalled
     └─restricted to versions 0.19.2 by an explicit requirement, leaving only ve
rsions 0.19.2

Discussion

Although the packages StatsBase and DataFrames appear in the above error message, the cause of this problem was actually the package Distributions.

Insensitive Laptop Touchpad

Mon, 06 May 2019 15:58:43 +0200

Problem

The touchpad on my new Ubuntu 18.04 LTS laptop was frozen. Toogling 🖱 with <Fn>-<F4> didn’t worked.

Attempt

Logout: didn’t work at all
Reboot: worked most of the time

Partial solution

After changing the Mouse Click Emulation in Keyboard & Mouse in Ubuntu Tweak from the default “Fingers” (2 fingers for right click; 3 fingers for middle click) to “Area” (Right/middle click determined by clicked area), one might have to wait for next reboot.

Juno Installation 2019

Mon, 06 May 2019 13:47:19 +0200

Goal

To install Juno for convenient development in Julia.

Problem

After Juno installation, I received the following error.

Analysis

From the error message, the system had tried to find an executable file julia, which would then be executed by the shell /bin/sh. Nonetheless, it’s absent from the system’s environment $PATH, so Juno couldn’t find it.

I’ve only changed my $PATH in ZSHRC, which is user-specific.

Solution

This Stack Overflow question about $PATH setting on *nix has provided various solution. As I was in a hurry to get Julia run on Juno, I’ve taken the advice from the best answer. I prefer creating a separate shortcut under /usr/bin, rather than editing system-wide config files.

Conditional Batch File Editing

Wed, 01 May 2019 23:56:44 +0200

Problem

During the adoption of Mmark for math posts on this blog, I had to insert markup: mmark at the last line of front matter of the source file of each math post.

Seek help

I separated this into two SO questions

Solution

From #1., I learnt the use of variables in AWK scripts. From #2, some users explained how these variables can be used for multi-line regex search.

My Intended Trigo Answer

Wed, 01 May 2019 22:24:45 +0200

The Math.SE question $2\cos(2x) - 2\sin(x) = 0$ has attracted several answers from high-rep users.

I am expanding @rhombic’s comment into an answer.

$$ \begin{aligned} 2\cos(2x)-2\sin(x)&=0 \\ 2 - 4\sin^2(x)-2\sin(x)&=0 \\ 2\sin^2(x)+\sin(x) - 1&=0 \\ (2 \sin(x) - 1)(\sin(x) +1) &= 0 \\ \sin(x) = \frac12 \text{ or } \sin(x) &= -1 \\ x = \frac{\pi}{6}, \frac{5\pi}{6} \text{ (rejected) or } & \frac{3\pi}{2} \text{ (rejected)} \end{aligned} $$

Improved Integration of Hugo and $\KaTeX$

Mon, 29 Apr 2019 09:48:32 +0200

Problem

There’s no custom $\KaTeX$ macro in local preview since I’ve merged some recent commits from the upstream of this blog’s theme, in particular, Beautiful Hugo’s pull requests #246 and #255, which allowed self-hosting the theme’s static JS, CSS and font files. This self-hosted option is particularly useful in case of slow response from Cloudflare’s CDN.

Even they do appear on the public GitLab site, the final rendered Markdown + $\TeX$ code would be succumb to syntax errors due to their absence in the preview process.

JavaScript Copy Button

Fri, 26 Apr 2019 23:01:53 +0200

Goal

To create a copy button for my Math.SE comment template in order to save the trouble of copying and pasting.

My first attempt

I put the boilerplate inside a Markdown codeblock to prevent them from getting interpreted by Hugo’s Markdown parser. Under each codeblock, I placed the copy button.

Comment boilerplate goes here ...

Another comment boilerplate goes here ...

…

My page’s original layout

$(document).ready(function() {
  $('.copyBtn').click(function() {
    copy($(this).prev().children())
j  });
});

function copy(selector) {
  var screenTop = $(document).scrollTop();
  var $temp = $("<div>");
  $("body").append($temp);
  $temp.attr("contenteditable", true)
       .html($(selector).html()).select()
       .on("focus", function() { document.execCommand('selectAll',false,null) })
       .focus();
  document.execCommand("copy");
  $temp.remove();
  $('html, body').scrollTop(screenTop);
}

static/js/copyBtn.js at Git tag copyBtn0

My Dual Answer

Fri, 26 Apr 2019 18:01:13 +0200

Update: The question has been reopened.

I intended to answer 김종현’s problem on Math.SE. However, the programs in the question body aren’t typeset in MathJax. As a result, I downvoted and closed this question because found it unclear. From the proposed dual, it seems that I shouldn’t interpret the primal as a linear program. Anyways, without further clarifications from OP, I found no reason to look at this further. Here’s my intended answer:

Finite Population Sampling without Replacement

Fri, 26 Apr 2019 09:46:29 +0200

First moment

Population: $ \Omega = \{ x_1, \dots, x_N \} $
Collection of $n$-samples: $\mathcal{S} = \{ s \in \Omega^n \mid \forall i,j \in s, i \ne j \} $
Collection of $n$-samples containing $x$: $ \mathcal{S}_x = \{ s \in \mathcal{S} \mid x \in s \} $
Observe that $ |\mathcal{S}_x| = \binom{N-1}{n-1} $.
Let population mean be zero. $\mu = 0$, i.e. $ \sum_{i = 1}^N x_i = 0 $
Fix an order for $\mathcal{S}$: $ \mathcal{S} = \{ s_1, s_2, \dots, s_{|\mathcal{S}|} \} $.
$j$-th $n$-sample mean $ m_j = \frac1n \sum_{x \in \mathcal{S}_j} x $
Remark: I don’t use $ \sum s_j $ as in $ \cup \mathcal{T} $ in topology to avoid misreading the $n$-sample $ s_j $ as an element.
mean of $n$-sample mean $ m = \frac{1}{|\mathcal{S}|} \sum_{s_j \in \mathcal{S}} m_j $

Replacing Deprecated Hugo Syntax in Blog Theme

Thu, 25 Apr 2019 12:45:08 +0200

Problem

Since the recent Hugo upgrade to v0.55.3, the following messages popped up after each local site regeneration with hugo server.

WARN 2019/04/24 18:07:00 Page's .URL is deprecated and will be removed in a futu
re release. Use .Permalink or .RelPermalink. If what you want is the front matte
r URL value, use .Params.url.
WARN 2019/04/24 18:07:00 Page's .Hugo is deprecated and will be removed in a fut
ure release. Use the global hugo function.
WARN 2019/04/24 18:07:00 Page's .RSSLink is deprecated and will be removed in a 
future release. Use the Output Format's link, e.g. something like: 
    {{ with .OutputFormats.Get "RSS" }}{{ .RelPermalink }}{{ end }}.
Total in 136 ms

GitLab’s online runner also gave the same type of warnings. This was reported in Beautiful Hugo issue #261.

Julia Rcall Installation

Wed, 24 Apr 2019 15:14:52 +0200

Problem

During the installation of RCall.jl, the package wasn’t successfully built due to a missing variable $R_HOME.

$ julia -q
julia> Pkg.add("RCall")
 Resolving package versions...
 Installed WinReg ─ v0.3.1
 Installed RCall ── v0.13.2
  Updating `~/.julia/environments/v1.0/Project.toml`
  [6f49c342] + RCall v0.13.2
  Updating `~/.julia/environments/v1.0/Manifest.toml`
  [6f49c342] + RCall v0.13.2
  [1b915085] + WinReg v0.3.1
  Building RCall → `~/.julia/packages/RCall/ffM0W/deps/build.log`
┌ Error: Error building `RCall`:
│ ERROR: LoadError: R_HOME is not a directory.
│ Stacktrace:
│  [1] error(::String) at ./error.jl:33
│  [2] top-level scope at logging.jl:322
│  [3] top-level scope at /home/vin100/.julia/packages/RCall/ffM0W/deps/build.jl
:19
│  [4] include at ./boot.jl:317 [inlined]
│  [5] include_relative(::Module, ::String) at ./loading.jl:1041
│  [6] include(::Module, ::String) at ./sysimg.jl:29
│  [7] include(::String) at ./client.jl:388
│  [8] top-level scope at none:0
│ in expression starting at /home/vin100/.julia/packages/RCall/ffM0W/deps/build.
jl:10
└ @ Pkg.Operations /buildworkjr/worker/package_linux64/build/usr/share/julia/std
lib/v1.0/pkg/src/operations.jl:1069

Discussion

It took me a few minutes to realise that the cause of this error is the absence of R. I referred to CRAN’s installation instructions for Ubuntu and added

Xubuntu Screen Enlargement

Sun, 21 Apr 2019 02:49:09 +0200

Tonight, the screen of Xubuntu suddenly enlarged and blurred. Typing “xubuntu screen display enlarged” on Google, I’ve learnt that the <Alt> key and the mouse scroll wheel can enlarge/minify screen display from Ubuntu Forums.

Cython Can't Replace Julia

Wed, 17 Apr 2019 16:57:32 +0200

This is a linklog to Christopher Rackauckas’s article about Julia, Cython & Numba. Unluckily, I don’t have time to read this now. Hope I can return to this later.

Cantonese vs Mandarin for Reading Tang Poems

Wed, 17 Apr 2019 15:12:31 +0200

This is a linkblog to a post on Discuss HK which claims how Mandarin (普通話) messes up the flat and oblique tones (平仄) of the regulate verse (近體詩) below.

《山行》　杜牧
遠上寒山石徑斜，白雲生處有人家。
停車坐愛楓林晚，霜葉紅於二月花。

Cantonese (粵語)	Mandarin (普通話)
仄仄平平仄仄平仄平平仄仄平平平平仄仄平平仄仄仄平平仄仄平	仄仄平平平仄平平平平仄仄平平平平仄仄平平仄仄仄平平仄仄平

However, Kimery has checked the Mandarin pinyin (拼音) and (s)he doesn’t found such problem except for some characters with entering tone (入聲). Luckily, such characters are located at the odd numbered position of a verse. Eventually, (after considering other factors,) that won’t harm the variation of tones in principle.

Quels schémas à tester ?

Thu, 11 Apr 2019 11:49:01 +0200

Pour simuler les trajectoires d’une équation différentielle, le schéma le plus facile est l’un découvert par Euler.

Cependant, en espérant mettre ce que j’ai vu au cours de ma licence en pratique, j’ai cherché un peu sur des méthodes numériques pour les EDS sur Google, et je suis tombé sur un article écrit par Brian D. Ewald.

Les différences entre les schémas « forts » et « faibles » seraient-ils pertinents pour mon stage ? On va voir.

Borel Cantelli Exercise 2019

Mon, 04 Feb 2019 16:24:40 +0100

I intend to post this for a Borel-Cantelli lemma exercise on Math.SE.

The target event is ${\exists i_0 \in \Bbb{N} : \forall i \ge i_0, X_i = 1}$, whose complement is

$$ {\forall i_0 \in \Bbb{N} : \exists i \ge i_0, X_i > = 0} = \limsup_i {X_i = 0}. $$

To apply Borel-Cantelli, one has to determine whether $\sum_i P(X_i = 0)<+\infty$.

Mise à jour du template de lettre

Wed, 16 Jan 2019 15:04:54 +0100

Contexte

J’ai publié mon template de lettre en Xe$\LaTeX$ sur mon ancien blog (hébergé sur GitHub Pages) il y a trois ans.

Problème et solution

Après le changement de l’ordi portable, il me faut l’installation du pacquetage “texlive-lang-french” sur la nouvelle version d’Ubuntu. Sinon, une erreur du pacquetage Babel se surviendra.

! Package babel Error: Unknown option `frenchb'. Either you misspelled it
(babel)                or the language definition file frenchb.ldf was not foun
d.

See the babel package documentation for explanation.
Type  H <return>  for immediate help.


l.445 \ProcessOptions*

?

A ce stade, Xe$\LaTeX$ parviendra à compiler le fichier $\TeX$ avec une remarque à propos de l’obsolescence de l’option frenchb pour le pacquetage Babel.

Staticman Failure on Tsalikis' Site

Tue, 01 Jan 2019 01:21:57 +0100

After reading Hugo Comments with Staticman on Kostas Tsalikis’ web site, I tried to leave the following comment.

As far as I know, Staticman can be used only with GitHub, since it works as a GitHub bot. Obviously, not all static sites are saved in GitHub, and this may be a showstopper for someone using another service. Thanks to eduardoboucas/staticman#219, Staticman now supports GitLab. You may view my demo Hugo site on Framagit at https://staticman-gitlab-pages.frama.io/bhdemo/posts/my-second-post/ Source) as a working example.

Staticman Repo Setup Errors

Tue, 25 Dec 2018 17:07:02 +0100

Background

Idem to Staticman on Framagit.

Besides, the build time for my Staticman + Beautiful Hugo demo on Framagit is half of that for the same project on GitLab.com.

Problem

After the setup, it’s possible that the theme shows “Sorry! There’s an error during submission.” To get an insight into this error, one has to open Web Developer Tools → Network and select the row corresponding to the POST request sent to the Staticman API. A side pane will pop out on the right. Select Response to view the API’s response in JSON.

Staticman's Encryption Mechanism

Tue, 25 Dec 2018 14:45:52 +0100

Background

Staticman’s documentation gives a link to the public key for the public Staticman instance.

I’ve set up my own Staticman instance for testing Staticman’s native GitLab support. It’s a coincidence that the public Staticman instance has been hitting it’s API limit, as reported in Staticman issue 227. To help others, I’ve published the URL of my own Staticman instance, which is associated with the GitHub/GitLab user staticmanlab. As Node.js’s RSA library has been used in Staticman, I have the responsibility to publish the public RSA key for my Staticman instance.

Staticman on Framagit

Mon, 24 Dec 2018 01:59:57 +0100

It’s a pity that some GitLab users have removed Staticman from their repo. I saw demand for Staticman from Framagit users. Therefore, after two days of testing, another API instance for Framagit has been created at https://staticman-frama.herokuapp.com. (Edit: typo edited, please see my comment below.)

The default GitLab base URL is set to “https://gitlab.com”. To provide Staticman support for a self-hosted GitLab service, another Staticman API server has to be set up.

I tried applying for OpenShift, but it’s been reported on Reddit that it takes about 10–20 days to get started. Amazon requires verification by credit card. I couldn’t deploy Staticman using Zeit Now’s Node.js server builder. Finally, I turned back to Heroku.

Detect Missing EOF

Sun, 23 Dec 2018 12:10:06 +0100

While editing files on GitHub/Gitlab, missing an empty line at the bottom of a file in the buffer will result in no newline at the end of file. In the case of regular text files, this isn’t consistent with the POSIX standards.

for file in `git ls-files`; do
  grep -Iq . $file && if ! newline_at_eof $file; then; else echo $file; fi
done

Fred has provided a shell script for detecting EOF on Stack Overflow. I’ve replaced bash with sh because I’m using Zsh.

Find Files for Rename

Sun, 23 Dec 2018 11:57:58 +0100

Background

Three years ago, I wrote Used More Bash Utilities for batch renaming files. One of my Facebook friends has pointed out that it fails for file names containing whitespace.

Problem

Recently, I would like to remove the extension name .sh of all shell scripts in ~/bin, so that which {script} will work without .sh.

Method

A for loop over $(ls) is a basic solution, but find is more correct since it’s possible that a file name contains a space character.

Comparaison of Two Docker Images for Hugo

Fri, 21 Dec 2018 21:56:57 +0100

Having importing the repo for the Hugo theme Introduction from GitHub to GitLab, I added the automatically generated GitLab CI config file and I ran job #135854407.

$ cd exampleSite
$ hugo --themesDir=../.. -d ../public
hugo: /usr/lib/libstdc++.so.6: no version information available (required by hugo)
hugo: /usr/lib/libstdc++.so.6: no version information available (required by hugo)

The build succeeded with the above message. To suppress it, a switch to another CI runner will do. The associated GitLab CI config file was copied from Hugo’s documentation with some customizations for Hugo sample sites

Advanced Git

Thu, 20 Dec 2018 08:29:17 +0100

Here goes more advanced Git commands not found among the basic ones.

for-each-ref

Display info in .git/refs.

#!/bin/sh

git for-each-ref --shell --format="ref=%(refname)" refs/tags | \
while read entry
do
  eval "$entry"
  echo `dirname $ref`
done

This modified example taken from the one in the official manual pipes

ref=refs/tags/181116
ref=refs/tags/copyBtn0
ref=refs/tags/fa531
ref=refs/tags/solarized

to a while loop. In each iteration, the read command reads each line in the piped output and sets it into the variable entry. The command will exit normally unless it meets an EOF, so that the code inside can be executed. The variable eval set the shell variable ref to the output Git reference name. dirname chops off the tag names (181116, fa531, etc) and returns refs/tags.

Git URL Shortener Exception

Wed, 19 Dec 2018 18:10:04 +0100

Due to limitations on the number of characters imposed by the site owner, URL shorteners are useful for shortening comments containing URL(s). Nonetheless, while commenting on my recent PR for Introduction, I found that GitHub’s URL shortener had lengthened the URL for GitHub’s home page.

Output of "https://github.com" by GitHub's URL Shortener

A counterexample of GitHub's URL Shortener

Compare these two URLs.

https://github.com
https://git.io/xE9D

Staticman Invitation is Case Sensitive

Wed, 19 Dec 2018 16:08:19 +0100

HTML and URL links are case insensitive. For example, GOOGLE.COM and google.com give the same address. As a result, after creating my fork of Beautiful Jekyll, I invited @staticmanlab to join my GitHub repo by firing the URL

https://staticman3.herokuapp.com/v3/connect/github/vincenttam/beautiful-jekyll

but I got

Failed Staticman invitation

The case for GitHub user name doens't match

Successful Staticman invitation

The case for GitHub user name match

SCSS to SASS Converter

Wed, 19 Dec 2018 01:56:58 +0100

Background

While porting Minimal Mistakes and Beautiful Hugo’s Staticman support to Introduction, I searched for “SCSS to SASS” on DuckDuckGo. The search engine returned results on “CSS to SASS/SCSS” or vice versa. The first theme has Staticman code in SCSS. That would fit into the third theme’s directory structure, which puts SASS files under assets/sass. However, SASS doesn’t have curly braces {}. I feared that after hours of tedious manual replacement, the code would fail to run. As a consequence, I conducted such Internet search.

Math.SE Comment Templates

Tue, 11 Dec 2018 12:38:28 +0100

Here’s a list of common comments for Math.SE newbies.

I’ve posted them on WordPress.com, but I often got typos after updating that page. Without version control, it’s hard to find out the cause of such error.

Questions lacking context

[Welcome to Math.SE!](//math.meta.stackexchange.com/a/11168/290189) Please read [this post](//math.meta.stackexchange.com/a/9960/290189) and the others there for information on writing a good question for this site. In particular, people will be more willing to help if you [edit] your question to include some motivation, and an explanation of your own attempts.

Questions not written in MathJax

[Welcome to Math.SE!](//math.meta.stackexchange.com/a/4928/290189) Please use MathJax.  For some basic information about writing math at this site see e.g. [basic help on MathJax notation](/help/notation), [MathJax tutorial and quick reference](//math.meta.stackexchange.com/q/5020/290189), [main meta site math tutorial](//meta.stackexchange.com/a/70559/259305) and [equation editing how-to](//math.meta.stackexchange.com/q/1773/290189).

Newbies’ combo

[Welcome to Math.SE!](//math.meta.stackexchange.com/a/11168/290189) [Please use MathJax.](//math.meta.stackexchange.com/a/4928/290189)  For some basic information about writing math at this site, see [MathJax tutorial and quick reference](//math.meta.stackexchange.com/q/5020/290189) and [equation editing how-to](//math.meta.stackexchange.com/q/1773/290189). Please read [this post](//math.meta.stackexchange.com/a/9960/290189) for writing a good question.

Newbies’ pic-question

To avoid excedding the upper limit of 500 characters, I’ve copied and pasted several comments and combined them into one.

Weak LLN Practice

Sun, 02 Dec 2018 08:11:56 +0100

My intended answer to a weak LLN problem on Math.SE.

Problem: Suppose $(X_n)$ is a sequence of r.v’s satisfying $P(X_n=\pm\ln (n))=\frac{1}{2}$ for each $n=1,2\dots$. I am trying to show that $(X_n)$ satisfies the weak LLN.

The idea is to show that $P(\overline{X_n}>\varepsilon)$ tends to 0, but I am unsure how to do so.

My solution: As in the accepted answer in OP’s previous question https://math.stackexchange.com/q/3021650/290189, I’ll assume the independence of $(X_n)$. By Chebylshev’s inequality,

Staticman Lab New Logos

Wed, 21 Nov 2018 08:31:23 +0100

StaticmanLab's new logo

GitLab logo recreated from Wikimedia's logo by Darby under CC-BY-SA 4.0 and Staticman logo on GitHub by Erlen Masson under MIT.

The old icon for Staticman Lab was made by GIMP from Staticman’s icon in PNG in the GitHub repo. Recently, I’ve found the SVG version of this icon. To serve customers better, I’ve recreated the logo from this SVG file so that the edges in the logo become sharper.

About me

Tue, 20 Nov 2018 15:10:10 +0100

A math student and a GNU/Linux user, built @staticmanlab on GitLab and GitHub.

Useful math links

Useful tech links

My jyutping generator
Google Advanced Search Form - Google Guide
Online Cangjie Input (and others like Pinyin, Quick, and Jyutping)
MATLAB–Python–Julia cheatsheet — Cheatsheets by QuantEcon documentation
R vs Julia cheatsheet - datascience-enthusiast.com
BitDegree’s cheatsheets
Online compilers and terminals on Tutorials Point
Web development Support tables

My online graphs

My presentations

Games

My tweak on Spaceball Cadet’s GitHub Page port.

Solution to a $p$-test Exercise

Tue, 20 Nov 2018 12:09:46 +0100

I intended to answer Maddle’s $p$-test question, but T. Bongers has beaten me by two minutes, so I posted my answer here to save my work.

The problem statement

This is the sum: $$\sum\limits_{n=3}^\infty\frac{1}{n\cdot\ln(n)\cdot\ln(\ln(n))^p}$$ How do I tell which values of $p$ allow this to converge? The ratio test isn’t working out for me at all.

Unpublished solution

The integral test will do.

$$ \begin{aligned} & \int_3^{+\infty} \frac{1}{x\cdot\ln(x)\cdot\ln(\ln(x))^p} \,dx \\ &= \int_3^{+\infty} \frac{1}{\ln(x)\cdot\ln(\ln(x))^p} \,d(\ln x) \\ &= \int_3^{+\infty} \frac{1}{\ln(\ln(x))^p} \,d(\ln(\ln(x))) \\ &= \begin{cases} [\ln(\ln(\ln(x)))]_3^{+\infty} & \text{if } p = 1 \\ \left[\dfrac{[\ln(\ln(x))}{p+1}]^{p+1} \right]_3^{+\infty} & \text{if } p \ne 1 \end{cases} \end{aligned} $$

When $p \ge 1$, the improper integral diverges. When $p < 1$, it converges.

Merge GitHub Pull Requests

Sun, 18 Nov 2018 01:05:42 +0100

Aim

To merge a pull request.

How?

Let’s take Staticman PR 231 as an example. I would like to test it before commiting this merget to Heroku.

$ cd ~/staticman
$ git branch -a
* deploy
  dev
  master
  ...
$ git remote -v
eduardoboucas https://github.com/eduardoboucas/staticman.git (fetch)
eduardoboucas https://github.com/eduardoboucas/staticman.git (push)
heroku  https://git.heroku.com/staticman3.git (fetch)
heroku  https://git.heroku.com/staticman3.git (push)
...
$ git pull eduardoboucas pull/231/head:deploy
remote: Enumerating objects: 10, done.
remote: Counting objects: 100% (10/10), done.
remote: Total 18 (delta 10), reused 10 (delta 10), pack-reused 8
Unpacking objects: 100% (18/18), done.
From https://github.com/eduardoboucas/staticman
 ! [rejected]        refs/pull/231/head -> deploy  (non-fast-forward)

I executed the last command on branch dev. I didn’t have time to figure out the reason for this error. The following commands should work.

Nested Comments in Beautiful Hugo

Sat, 17 Nov 2018 15:12:50 +0100

Quick links

Motivation

For the mathematical ones, please see my previous post.

As a math student, it’s inefficient to reinvent the wheel like engineering students. Thanks to three existing examples, I had convinced myself that I could bring this to the theme Beautiful Hugo.

Zongren’s Hexo theme (worked best)
Made Mistakes Jekyll theme
Network Hobo’s customization of Beautiful Hugo (inspired by the second one, but contains a logic error)

Interactive Blog on Static Web Host

Sat, 17 Nov 2018 10:09:12 +0100

Vision

gain autonomy: freedom is the basis of moral actions. No freedom, no morality.
transcend ourselves: change/improve our lives through free thoughts

Goal

Convert our free thoughts into free code.

Free code allows users around the world to run and/or improve them. This would bring real enhancement to our tools.

For example, beautiful math writing used to be a complicated process. A decade ago, this required the installation of a typesetting engine called $\LaTeX$. Thanks to freely available scripts like MathJax and $\KaTeX$, it’s now possible to write math viewable by any modern web browser by writing the content in the middle.

Simplex Calculations for Stokes' Theorem

Sat, 03 Nov 2018 02:05:58 +0100

Oriented affine $k$-simplex $\sigma = [{\bf p}_0,{\bf p}_1,\dots,{\bf p}_k]$: A $k$-surface given by the affine function
$$ \sigma\left(\sum_{i=1}^k a_i {\bf e}_i \right) := {\bf p}_0 + \sum_{i=1}^k a_i ({\bf p}_i - {\bf p}_0) \tag{1}, $$

where ${\bf p}_i \in \R^n$ for all $i \in \{1,\dots,k\}$.
In particular, $\sigma({\bf 0})={\bf p}_0$ and for each $i\in\{1,\dots,k\}$, $\sigma({\bf e}_i)={\bf p}_i$.
Standard simplex $Q^k := [{\bf 0}, {\bf e}_1, \dots, {\bf e}_k]$: A particular type of oriented affine $k$-simplex with the standard basis $\{{\bf e}_1, \dots, {\bf e}_k\}$ of $\R^k$.
$$ Q^k := \left\{ \sum_{i=1}^k a_i {\bf e}_i \Biggm| \forall i \in \{1,\dots,k\}, a_i \ge 0, \sum_{i=1}^k a_i = 1 \right\} $$

Note that an oriented affine $k$-simplex $\sigma$ has parameter domain $Q^k$.

La norme lipschitzienne est complète

Fri, 02 Nov 2018 23:50:57 +0100

Dans l’article de Robert Fortet et Edith Mourier en 1953, une distance entre deux mesures de probabilité sur un espace métrique est définie.

De nos jours, je trouve la façon dont ils l’ont écrit assez difficile à comprendre. Je suis plus à l’aise avec $\sup$ que “b.s.” que désigne “borne supérieure”. Ils se sont servi de $M[f]$ pour $\lVert f \rVert_{\rm Lip}$, où

$$ \lVert f \rVert_{\rm Lip} = \sup_{x \ne y} \frac{|f(x) - f(y)|}{d(x, y)}. $$

Mesurabilité des réalisations trajectorielles

Thu, 11 Oct 2018 23:20:37 +0200

Notations

Supposons toutes les notations dans Espace de trajectoires.

Problématique

La mesurabilité de l’application dans le sous-titre est basée sur l’égalité suivante.

$$ \Bor{\R}{\OXT} \cap \CO = \Bor{\CO} $$

J’ai passé quatres heures pour comprendre

pourquoi ça entraîne la mesurabilité ?
pourquoi l’égalité elle-même est vraie ?

Réponses

Mesurabilité de la trace sur $\CO$ de $\Bor{\R}{\OXT}$

A la première lecture, je ne connaisais même pas la définition de la trace d’une tribu sur un emsemble. En effet, c’est une définition universaire sur des ensembles, selon une question sur la trace sur Math.SE.

What are Dataframes?

Sun, 07 Oct 2018 17:30:49 +0200

Motivation

The books that I read in the past didn’t explain what a dataframe meant.

Definition

Dataframe: A table of data in which the values of each observed variable is contained in the same column.

Counterexample

I’ve difficulty in reading long lines of text like the above definition, so let’s illustrate this definition with a counterexample.

We have carried out repeated experiments with four types of things and obtaine some data. (Say, poured some liquid into an empty cup and take the temperature.)

Enlarged /var Partition

Sat, 06 Oct 2018 08:02:36 +0200

Background

I’ve installed Ubuntu 18.04 on my new laptop.

Problem

The /var partition was too small. The system complained that only 200 MB was left.

Solution

Rebooted with my live USB.
Opened GParted.
Moved /tmp partition to the left and grew it to 6 GB.
Grew /var partition to 16 GB
Click

Results

Details [TL;DR]

Here’s the GParted generated log.

Ultrafilters Are Maximal

Fri, 05 Oct 2018 13:19:36 +0200

Ultra filter: A filer $\mathcal{F}$ containing either $Y$ or $Y^\complement$ for any $Y \subseteq X$.

Two days ago, I spent an afternoon to understand Dudley’s proof of this little result.

A filter is contained in some ultrafilter. A filter is an ultrafilter iff it’s maximal.

At the first glance, I didn’t even understand the organisation of the proof! I’m going to rephrase it for future reference.

only if: let $\mathcal{F}$ be an ultrafilter contained in another filter $\mathcal{G}$. If $\mathcal{F}$ isn’t maximal, let $Y \in \mathcal{G} \setminus \mathcal{F}$. Since $\mathcal{F}$ is an ultrafilter, either $Y \in \mathcal{F}$ or $Y^\complement \in \mathcal{F}$. By construction of $Y$, only the later option is possible, so $Y^\complement \in \mathcal{G}$ by hypothesis, but this contradicts our assumption $Y \in \mathcal{G}$: $\varnothing = Y \cap Y^\complement \in \mathcal{G}$, which is false since $\mathcal{G}$ is a filter.

2018-10-04 Seminar Notes

Thu, 04 Oct 2018 02:16:44 +0200

I jotted down only a few keywords that might be reusable. I didn’t understand any of the talks.

Functional Data Analysis

Goal: predict equipment temperature
Tools: Fourier coefficients (trigo ones), followed by discretisation, min-error estimation, cross-validation 10-folds, $R^2$ adjusted ?, MAE, MSPE
Comparison with non-functional data

Tolérancement

Thème : Traiter les incertitudes sur les dimensions des pièces de l’avion
Objectif :
- établir une modélisation mathématiques
- construire un virtual twin de l’avion
Outils :
- Modèle de variabilité
- Modèle d’assemblage $\text{airbus}: Y = \sum_{i = 1}^n a_iX_i?$
- Notion de risque … calculs des coefficients de convolution

SVM

Multiclass vs structual, hidden Markov model
Plan for this year:
- apply structual SVM for real SVM
- apply structual SVM for deep neural network

Auxiliary information

auxiliary function given in one partition
auxiliary function given in mutiple partitions
bootstrap
law of iterated logarithms
Kullback–Leibler distance
convergence: Donsker class, var, covar
ranking ration method: convergence to Gaussian process, entropy conditions, Telegrandś inequality
- weak convergence: KMT, Berthet-Maison
- strong convergence: ?
  - consequences: Berry-Essen bound, bias & variance estimation of ranking ration method

Euler scheme SDE

I could only write “Toeplitz tape operator”.

Measures Are Regular

Wed, 03 Oct 2018 22:28:34 +0200

Problem

To show that a measure $\mu$ defined on a metric space $(S,d)$ is regular.

outer regularity: approximation by inner closed sets
inner regularity: approximation by outer open sets

Discussion

Since this problem involves all borel sets $A \in \mathcal{B}(S)$, the direct way $\forall A \in \mathcal{B}(S), \dots$ won’t work. We have to use the indirect way: denote $$\mathcal{C} = \lbrace A \in \mathcal{B}(S) \mid \mathinner{\text{desired properties}} \dots \rbrace.$$ Show that

Filters and Nets

Wed, 03 Oct 2018 11:27:55 +0200

Motivation

$$ \gdef\vois#1#2{\mathcal{V}_{#1}(#2)} $$

Nets and filters are used for describing convergence in a non-metric space $X$.

Denote the collection of (open) neighbourhoods of $x \in X$ by $$\vois{X}{x}$$.

Definitions and examples

Directed set

A partially ordered set $I$ such that $$\forall i, j \in I: i \le j, \exists k \in I: k \ge j.$$

Net

A function in $X^I$, where $I$ is a directed set.

example: any sequence in $X^\N$

Convergence of nets to a point

$x_i \to x$ if $$\forall A \in \vois{X}{x}, \exists j \in I: \forall k \ge j, x_k \in A.$$

example: absolute convergence of series ($I$ is the collection of finite subsets of $\N$, finite sum $\Sigma \in \R^I$.)
example: Riemann integral ($I$ is the collection of tagged partitions, the partial order doesn’t depend on tags, $\int \in \R^I$.)

Filter base

A nonempty collection $\mathcal{F} \subseteq \mathcal{P}(X) \setminus {\varnothing}$ such that $$\forall F,G \in \mathcal{F},\exists H \in \mathcal{F}: H \subseteq F \cap G.$$ (contains nonempty part of intersection)
Difference with topological basis: sets have to be nonempty here

Filter

A filter base $\mathcal{F}$ so that

contains supersets: $\forall F \in \mathcal{F}, \forall G \supseteq F, G \in \mathcal{F}$
contains intersection: $\forall F, G \in \mathcal {F}, F \cap G \in \mathcal{F}$

The image of a filter $\mathcal{F}$ under a function $f$ is also a filter, denoted by $f[[\mathcal{F}]]$.

Cover Letter Organisation

Tue, 02 Oct 2018 21:50:02 +0200

I keep sentences below short and minimal for memory.

Sender’s contact info at top-right hand corner, followed by receipent’s contact info left-aligned.
“I’m …”, “apply for …, as advertised in …”
Why apply? Link with the company(’s employee)
Pastimes (all-rounded person), continual learning (for useful skills)
Friendly, polite and to-the-point sign-off
Signature followed by sender’s name

Minimal Jekyll Site with Static Comments

Sun, 30 Sep 2018 23:59:14 +0200

Introduction

This is the GitHub Pages version to my GitLab Pages with Staticman tutorial.

I didn’t plan to test whether Staticman v3 work on GitHub since it’s proprietary. However, from Staticman issues #222 and #227, we know that the official server doesn’t respond to

GET /v2/connnect/<USERNAME>/<REPONAME>

To help others, I self-advertised my own Staticman API instance and the migration to GitLab pages. Unfortunately, nobody had managed to create a GitHub repo running on my API instance. To convince others that it’s also working on GitHub, I decided to create a minimal GitHub repo.

Espace de trajectoires

Fri, 28 Sep 2018 10:41:32 +0200

Tribu produit

source	symbole	engendrée par
Prof	$\Er{\OXT}$	$\mathcal{C}_0 = \Big\lbrace \lbrace f \in E^\Bbb{T} \mid f(t) \in B \rbrace \bigm\vert t \in \Bbb{T}, B \in \Er \Big\rbrace$ $\mathcal{C}_1 = \Big\lbrace \lbrace f \in E^\Bbb{T} \mid f(t_i) \in B_i \forall i \in \lbrace 1,\dots,n \rbrace \rbrace \newline \bigm\vert t_j \in \Bbb{T}, B_j \in \Er \forall j \in \lbrace 1,\dots,n \rbrace, n \in \N^* \Big\rbrace$
Meyre	$\bigotimes_{t \in \Bbb{T}} \Er$	des cylindres $C = \prod_{t \in \Bbb{T}} A_t$ d’ensembles mesurables $A_t \in \Er$ de dimension finie $\card{\lbrace t \in \Bbb{T} \mid A_t \neq E \rbrace} < \infty$

Je trouve $\Er{\OXT}$ plus court à écrire, tandis que $\bigotimes_{t \in \Bbb{T}} \Er$ est plus flexible.

Real Number Construction From Dedekind Cuts

Thu, 27 Sep 2018 20:48:40 +0200

Goal

To gain a real understanding on real numbers.

Analytical construction

I “swallowed” the Compleness Axiom, then I worked on exercises on $\sup$ and $\inf$, and then the $\epsilon$-$\delta$ criterion for limits, before completing $\Q$ with Cauchy sequences.

I’ve also heard about the completion of a metric space in a more general setting. My professor once said that it suffices to view this proof once throughout lifetime: the proof itself wasn’t very useful.

The basic arithmetic properties of $\R$, as an equivalence class of Cauchy sequences sharing the same limits, didn’t arouse our interests. That’s just an extension of its rational counterpart due to some arithmetic properties of limits.

Custom $\KaTeX$ Macros

Thu, 27 Sep 2018 19:32:58 +0200

Background

Same as the last section in Beautiful Hugo Improvements.

Goal

To write math efficiently by automatically loading longer code with shorter macro code.

For example, when I wrote Some Infinite Cardinality Identities, it would be ten times more quicker and efficient to type \card{C} than to write \mathop{\mathrm{card}}(C) all the time.

Changes committed to my repo

The current version of Beautiful Hugo is still using $\KaTeX$ v0.7, which doesn’t support macros in auto-rendering. It would be inconvenient to include the macros after invoking $\KaTeX$’s render function.

Better Hugo ToC Fix

Thu, 27 Sep 2018 18:56:40 +0200

Background

I applied a fix to Hugo’s ToC ten days ago.

Drawbacks

To make the script non-render blocking, one has to place it in the footer. As a result, it takes about 0.2 seconds to remove the excess <ul> tag.

Solution

Thanks to Beej126’s Hugo template code, this site delivers table of contents processed by Hugo during GitLab’s continuous deployment.

Some Infinite Cardinality Identities

Tue, 25 Sep 2018 23:02:24 +0200

Purpose

This post aims at recapturing the main ideas of the formal proofs that I’ve read. It never tries to replace them. You may consult the references if you need any of them.

Some notations

Unless otherwise specified, all cardinalities here are infinite. Denote $\mathfrak{a} = \card{A}$, $\mathfrak{b} = \card{B}$ and $\mathfrak{i} = \card{I}$.

Sum: $\mathfrak{a} + \mathfrak{b} = \card{A \cup B}$ provided that $A \cap B =\varnothing$.
Product: $\mathfrak{a} \, \mathfrak{b} = \card{A \times B}$
Power: $\mathfrak{a}^\mathfrak{i} = \card{A^I}$, where $A^I = \lbrace f \mid f: I \to A \rbrace$ denotes the set of functions from $I$ to $A$.

I've chosen $I$ instead of $B$ to express the index set because this reminds me of an array of $(a_i)_i$ indexed by $I$.

Install Julia From Source

Sat, 22 Sep 2018 21:38:43 +0200

Goal

To get Julia installed as a normal user on RHEL 6.

Motivation

“Julia talks like Python but walks like C.”

To do statistics more efficiently.

The compiled binaries often contain install scripts which put files to shared folders under /usr. Consequently, they have to be run as sudo privileges. That drove me to start this lengthy Julia compilation.

Installation

Without sudo privileges, I’ve chosen to compile Julia from source. I was too lazy to get the dependencies fixed. I just compiled it without GFortran and pkg-config under the ~/src folder.

My First RHEL Experience

Thu, 20 Sep 2018 21:47:02 +0200

Introduction

This article records my errors and difficulties encountered on the first day I came across Red Hat Enterprise Linux 7 in my school’s laboratory, as a normal user without sudo privileges.

The login screen was gdm, and the desktop environment was GNOME. IBus was used as the input engine.

Packages installed

The principal goal is to install tools that I usually use on RHEL without sudo permissions. To do so, I’ve downloaded the executable binaries or source code of these packages. As I wanted to focus on my studies, I prefer downloading executable binaries.

$\pi$–$\lambda$ Theorem

Wed, 19 Sep 2018 15:56:35 +0200

Statement

Slogan version

$$\sigma = \pi + \lambda$$

$\sigma$ $\pi$ $\lambda$

“sum” “product” “limit”

universe nonempty universe

complement complement

countable union finite intersection disjoint countable union

A $\sigma$-algebra is a $\pi$-system and a $\lambda$-system, and vice versa.

$\sigma$	$\pi$	$\lambda$
“sum”	“product”	“limit”
universe	nonempty	universe
complement		complement
countable union	finite intersection	disjoint countable union

Wiki version

A $\lambda$-system is a synonym of a Dykin system.

$$\mathcal{P} \subseteq \mathcal{D} \Longrightarrow \sigma(\mathcal{P}) \subseteq \mathcal{D}$$

Given a $\pi$-system contained in a $\lambda$-system. Then the $\sigma$-algebra generated by the $\pi$-system is also contained in the $\lambda$-system.

Staticman API Hosting 2018

Mon, 17 Sep 2018 22:00:07 +0200

Update: I suggest reading a newer tutorial for setting up your custom API server that works with GitHub Apps. The package maintainers suggest hosting your own API server.

Goal

To host an instance of Staticman v3 server on Heroku.

This post involves server-side setup of the commenting system. If you simply want to have a taste of this system on GitLab, you may try my demo GitLab Page.

I try to address some concerns about this API service in the introduction of this series to keep this page focused on the technical aspects of my customizations against staticman/dev branch.

Copy File and Preserve Path

Mon, 17 Sep 2018 12:39:09 +0200

Background

While making changes to a theme for a static site generator, I changed files under a Git submodule included in the repo for my blog. (e.g. themes/beautifulhugo) That’s ideal for local testing, but not for version control. As a result, I cloned the repo for the theme to a directory separate from the one for my bloge (say, ~/beautifulhugo), and commit the changes there, then performed a Git submodule update so as to make the workflow clean.

Fix Hugo Table of Contents

Mon, 17 Sep 2018 12:31:03 +0200

Background (TL;DR)

While setting up the new version of Staticman for my demo GitLab pages, I’ve read developers’ documentations, setup guide and some community blog posts so as to come up with my own guide. It’s originated and inspired from a variety of sources, and refined according to hours of testing. Consequently, despite the original intention to keep things simple, I’ve finally come up with a post with over a thousand words.

To pass my ideas in this post to visitors, it’s better that they have an overview of the contents before actually looking into the details. Therefore, a table of contents is nice-to-have feature for this blog.

Config GitLab Repo for Staticman

Sun, 16 Sep 2018 19:12:15 +0200

Update: I suggest reading a newer tutorial.

To keep focused on the technical setup, please refer to the introduction of this series for the reasons of choosing Staticman and GitLab.

Goal

To set up unauthenticated commenting system on GitLab pages.

Demo GitLab Page with Staticman v3

Built on 14/09/2018

This post aims at providing a walkthrough to the GitLab repo setup. If you want to host your own Staticman API instance, you may refer to the next post in this series.

Welcome to static comments

Sun, 16 Sep 2018 19:12:15 +0200

I put some “why” questions here so as to keep focus on the technical setup of the GitLab repo and the optional Staticman API server.

Why static blogs instead of dynamic ones?

quicker loading time
better reliability (can handle more request)
no database needed
greater control on content, styles and layout

Why static comments?

allow feedback from visitors
site owner owns the comment locally (unlike WordPress, Facebook, Disqus, etc)
- no remote database needed, so no need to worry server errors from third-party commenting services.
- greater control over the rendering of the comments (allow additional features such as Markdown syntax, and $\KaTeX$ support)
- more accessible since static comments are incorporated as HTML elements into the post. No JavaScript is required to retrieve the comments, contrary to most third-party commenting services.

Before Staticman’s deployment, another commenting system called Pecosys was already available. However, it’s less convenient to handle visitor’s requests as emails.

PDF Form Printing Error

Sun, 16 Sep 2018 01:57:12 +0200

Background

Le Temple du Marais

"Eglise verte" means "green church".

My churches are going green.

Problem

→ I downloaded a PDF from Haute-Garonne’s government site, filled in the form and saved it on a USB key. Then I printed it at a Konica Minolta bizhub photocopier yesterday.

However, _only_ the radio buttons and checkboxes were printed. The blanks were left _blank_! I opened my PDF and double-checked that I had input the text in .

Printed output

Printed by a Konica Monilta bizhub photocopier

Flying Grizzly's HTML Form Submission Error

Sat, 15 Sep 2018 23:09:06 +0200

Problem

I would like to submit Flying Grizzly’s form. I filled in every blanks and then I clicked the “submit” button below. I was greeted with a MISSING_REQUIRED_FIELDS error within a second.

HTML form

every entry filled in

Staticman v2 server response

500 internal server error

{
    "success":false,
    "data":["replying_to"],
    "rawError":{
        "_smErrorCode":"MISSING_REQUIRED_FIELDS",
        "data":["replying_to"]
    },
    "errorCode":"MISSING_REQUIRED_FIELDS"
}

Discussion

The error code suggested that the form fields sent should be inspected.

Beautiful Hugo Improvements

Wed, 12 Sep 2018 09:17:39 +0200

Fixed issue #142

Two weeks ago, Google Webmasters complained about the broken urls in this blog’s Tags page. This was reported by Joakim Vivas as issue #142 half a year ago. Pascal had submitted pull request #165 to fix this. However, he self-closed his PR.

Since the last commit by Michael Romero, Beautiful Hugo’s owner, was five months ago, it seems that he has abandonned his project. Therefore, I used Kaushal Modi’s solution to fix this at commit ff536782.

CJK on Ubuntu 18.04

Sun, 09 Sep 2018 00:33:53 +0200

Goal

To enable Chinese and Japanese input on (X)ubuntu 18.04 laptops .

My choices of input method

	old	new
OS	Xubuntu 18.04	Ubuntu 18.04
Desktop Environment	Xfce	GNOME
Input method	Fcitx	IBus

Language	Method
中文	Rime
日本語	Mozc

On my old Fujitsu laptop running Xubuntu, I’ve chosen Fcitx. This turns out to be a difficult choice when I install Rime.

Japanese input

Thanks to ひゃまだ, I’ve managed to switch between difference modes in Mozc.

Zsh and NPM Setup on Ubuntu

Thu, 06 Sep 2018 13:00:53 +0200

Problem

After installing NPM throught Ubuntu’s default apt-get manager, I got permission errors. Though sudo can solve the problem, that’s not the right way in principle because NPM is supposed to hold different versions of Node.js packages for testing. It’s insecure to execute npm with sudo priviledges.

Solutions

Install Zsh to improve efficiency

Grab Oh My Zsh to instal NVM as its plugin.

 sh -c "$(curl -fsSL https://raw.githubusercontent.com/robbyrussell/oh-my-zsh/master/tools/install.sh)"

Use NVM (NPM Version Manager) to manage NPM.

Towards Better File Management

Thu, 06 Sep 2018 11:05:53 +0200

Le Temple du Marais

"Eglise verte" means "green church".

Background: 🈶 ⛪ → 🌿

→ 📧 In the recent decade, organizations are replacing courrier with email. The reason is two-folded. 🌿 First, the later is more environmentally-friendly. 📨 Second, the later delivers the content to the recipient quick as a flash.

📧 📎 When one sends an email, one sometimes wants to attach a file to an email. If one has to sign a paper document and send it by email, then one will probably need a scanner. (Despite the emergence of scanning apps on mobile devices, the quality of a scanner is normally better since the page is flattened during the scan.)

Laptop Battery Life

Wed, 05 Sep 2018 23:13:45 +0200

Main ideas

– Ideal energy range for storage: 40%–80%
The biggest enemy of electronic parts is heat .
Avoid overchanging and unplug AC adapter when charging is complete. In particular, don’t leave a fully charged laptop connected to power supply. This can reduce the lifespan of the battery.
Avoid deep discharges: recharge the laptop battery when its enery level drops to 40%.
Reduce unnecessary programs running in background.
If your hardware vendor supports Linux drivers for batteries, set the charging thershold to 80%.
- Some Lenovo Thinkpads can benefit from those drivers.
- Other vendors like Fujitsu offers such drives for M$ Windows only.

External URLs

Sublime Text 3

Wed, 05 Sep 2018 20:52:51 +0200

Usual keys

I’ll only list those I find useful. See Sublime Text Unofficial Documentation’s list for a more comprehensive list.

<C-Up> / <C-Down>: move up ↑ / down ↓ without changing cursor position.
<C-g>: go to line number
<C-p>: go to other files
<C-S-p>: show Command Palette

Searching / Replacing

As usual, it supports custom selection range and regular expressions as expected. Transformations preserving cases are possible.

Missing Newline at EOL

Wed, 05 Sep 2018 00:31:02 +0200

Background

Despite my experience in Vim, the multi-cursor functionality in Sublime Text 3 has seduced my to change my editor.

Unlike Vim, a nonempty new line at the end of Sublime Text 3 file buffer causes the file to end without a newline character. In fact, it’s a POSIX standard to include a newline character at the EOL (end of file). (c.f. No Newline at End of File)

Problem

Unaware of the above POSIX standard and Sublime Text 3 convention, I have edited many lines of code in the repository for this blog and the one for my custom Beautiful Hugo. These edited files were almost everywhere in these repositories, and they polluted their remote counterparts on GitLab .

CSB Theorem

Wed, 29 Aug 2018 11:25:24 +0200

This isn’t a substitute for books .

Reminder

$A \preceq B$: $A$ can be “injected” into $B$.
$A \sim B$: $A$ and $B$ share the same cardinality.
$A \prec B$: $A$ can be “injected” into $B$, but it’s “smaller” than $B$.
A finite set can be “counted” from one to some nonnegative integer.
Infinite is the “antonym” of finite.

Wolf’s proof

When I first saw this proof in Robert S. Wolf’s Proof, Logic and Conjecture: The Mathematician’s Toolbox, I gave it up since it wasn’t as intuitive as the statement.

Bash Commands

Tue, 28 Aug 2018 17:18:27 +0200

This is a page for my personal reference. TLDR pages has a more comprehensive command collection.

Background settings

Take the local repo of this blog as an example.

Show current path.

$ pwd
/home/vin100/quickstart

Distinguish files from folders .

$ ls -l
total 28
drwxrwxr-x 2 vin100 vin100 4096 Jun 28 21:00 archetypes
-rw-rw-r-- 1 vin100 vin100 2734 Aug 28 17:30 config.toml
drwxrwxr-x 4 vin100 vin100 4096 Jun 29 00:47 content
drwxrwxr-x 3 vin100 vin100 4096 Aug 25 15:29 layouts
drwxrwxr-x 9 vin100 vin100 4096 Jun 29 00:47 public
drwxrwxr-x 4 vin100 vin100 4096 Aug 25 13:36 static
drwxrwxr-x 3 vin100 vin100 4096 Aug 27 18:06 themes

apg

Avanced password generator.

Brighten Image With GIMP

Thu, 23 Aug 2018 13:36:44 +0200

Motivation

One loves adding colors to his/her life by adding stunning photos to his/her social media profile. However, due to various constraints, such as weather, budget and time, it’s possible that the photos taken look dark and somber.

Eglise St Martine

Photo taken at Pont-du-Château, Puy-de-Dôme (63) on 30th June, 2017

Despite a suboptimal choice of camera angle, a right tool enables you to take the best out of the photo. Let’s go GIMPing.

Ubuntu 18.04 Installation on Fujitsu AH557

Sat, 18 Aug 2018 18:39:42 +0200

Objective

To get a hands-on experience on Ubuntu installation on a UEFI hybrid system.

Devices

120 GB SSD disk: /dev/sda
1 TB HDD disk: /dev/sdb
8 GB USB key: /dev/sdc

Stage 0: precautions

Ensure that your machine has enough power.
Disable Secure Boot in M$ Windows
Disable Quick Boot in boot menu

Stage 1: Make your live USB key

I tried Xubuntu’s built-in disk writing tool to create a live USB key from the official ISO file. Like my Xubuntu 18.04 installation on Fujitsu LH532 , the installer crashed during the installation. After submitting the generated report to Launchpad, I found out that the cause for this crash: the integrity test for my live USB key had failed.

TLP Prevents Login on Ubuntu 18.04

Wed, 15 Aug 2018 11:12:59 +0200

It’s FOSS’s after-installation guide #11 recommends TLP. However, this package stopped my laptop from shutting down and logging in. I resorted to remove it through TTY.

Web Image Optimisation with GIMP

Thu, 26 Jul 2018 10:52:48 +0200

Why image optimization?

To save loading .

My old way

ImageMagick provides a great CLI utility to convert and compress images for any purposes. However, to -crop images, I have to specify the numbers in pixels. One certainly works much more efficiently with a GUI tool.

My new way

GIMP can do anything that Adobe Photoshop can do, even saving images for web. In the linked page to this powerful GIMP plugin tutorial, the link for the GNU/Linux binary file is broken.

Fujitsu LH532 Keyboard Cleaning

Mon, 23 Jul 2018 15:43:01 +0200

😖 @ 📃! This post contains unpleasant images. If you don’t wish to see them, please view this page with a text browser or a text mode plugin of your browser.

Rationale

Why?

My Fujitsu LH532 has been serving me well as my production machine for almost six years.

The keyboard was quite dirty: it’s full of hair and dandruff. I had to clean it for personal hygiene.

Rodéo

Tue, 17 Jul 2018 11:40:17 +0200

au sens propre: (comme en anglais)

Un événement dans lequel un cavalier essaie de demeurer sur un cheval avec deux jambes levées.

Rodéo au sens propre

Source: Pixabay
au sens figuré dans l’actualité

Une façon dangereuse de conduite dont le conducteur lève la(les) roule(s) antérieure(s).

Rodéo au sens figuré

Source: Pixabay

Le dicto Collins a recordé une utilisation très rare de ce mot. Récemment, on l’utilise plus fréquemment en raison de la lutte contre les rodéos sauvages.

Hugo Image Path Refactoring

Sat, 14 Jul 2018 14:18:28 +0200

Goal

To set up a reasonable content structure for my blog.

Before Hugo

In my old Octopress blog, images and posts were placed under source/images/posts and source/_posts folders respectively. They were so far apart that I needed to use copy and paste the URL’s so as to get them right. As the size of the blog grew, I could hardly retrieve an image without first listing the files in the post image folder. This significantly reduced the efficiency of blog writing. In my hometown, people take efficiency seriously.

Combine PDF in Linux

Fri, 13 Jul 2018 17:30:54 +0200

pdfunite is fairly easy to use.

pdfunite PDF-sourcefile1..PDF-sourcefilen PDF-destfile

Another way is to use QPDF. I’ve learnt to add --empty from @qpdf/qpdf:#12.

qpdf --empty --pages *.pdf -- out.pdf

Brightness Key on Linux

Mon, 09 Jul 2018 23:21:17 +0200

Problem

One can use xrandr to adjust screen brightness. However, the factor (default to 1.0) is relative to the current brightness. How to enable the brightness adjust keys / on the keyboard under Xubuntu 18.04?

Solution

Toz’s post on Ubuntu Forum works like a charm. The default value for GRUB_CMDLINE_LINUX is an empty string. Changing it to acpi_backlight=vendor and updating the GRUB has solved the problem since the next boot.

Stow Your Dotfiles

Sun, 08 Jul 2018 16:01:22 +0200

I correctly set up the system configuration file manager GNU Stow and the version control system (VCS) Git on my Fujitsu Lifebook so that the former can automatically install system configuration files like modules, whereas the later can track the code in those files.

What I mean for correctly is that in the ssh folder of the remote dotfiles repo, there is neither SSH key files nor entries representing SSH keys in the gitignore file. You may view Jan Uhlik’s dotfiles on GitLab as an example.

Upgraded to Linux Mint 19

Sat, 07 Jul 2018 21:14:02 +0200

Rationale

My Linux Mint 18.3 installed on Clevo N240GU was a long-term support (LTS) version. Although the official page didn’t recommend an upgrade for its own sake, I still performed it as a result of my conversation with a technician in a computer store. He thought that the display problem in the current version would be fixed in this upgraded version.

The old version of Linux Mint couldn’t detect the onboard Intel graphics card. Therefore, sensors reported a higher CPU temperature and the display resolution couldn’t be correctly configured.

Fujitsu LH532 Fan Cleaning

Wed, 04 Jul 2018 20:52:37 +0200

Problem

Two months ago, the Win* 10 installed on my old laptop crashed with blue screen on startup. Two weeks ago, I created a Xubuntu 18.04 LTS 64-bit Live USB and set up the dualboot. However, the fan was still giving out consideralbe noise and heat under Xubuntu 18.04 (installed in /dev/sda7).

Many end users’ reaction

They’ll simply buy a new PC. This had given rise to industrial parks in Guiyu (貴嶼), one of the world’s largest e-waste village. I’m so shocked to see that Hong Kong appears on the top of the linked article.

Configure UFW for Hugo

Fri, 29 Jun 2018 06:36:21 +0200

Easy Linux tips project recommends users to enable their firewall. However, this blocks all incoming traffic by default. If one wants to test the site on mobile devices, one will need to add a few rules to UFW.

$ sudo ufw allow ssh
$ sudo ufw allow http
$ sudo ufw allow https
$ sudo ufw allow 80/tcp
$ sudo ufw allow 1313/tcp comment "hugo server"

I learnt the last line from 竹内電設.

Xubuntu Dualboot on Fujitsu LH532

Thu, 28 Jun 2018 21:50:45 +0200

You may skip to the acutal setup.

Background

After using Win 7 & 10 for six years on my Fujitsu LH532 , Windows 10 often falls into blue screen. Sometimes, it won’t even start up.

Give Xubuntu a try

Hoping to give a second life to my old , I’ve decided to try this popular lightweight distro.

Initial partition setup

I followed the instructions from Danatela’s question, including the optional setup of separate /var and /tmp partition.

Agencer

Tue, 26 Jun 2018 20:13:17 +0200

v. arranger, organiser

La cuisine est bien agencée.

My First Post

Sun, 24 Jun 2018 02:05:00 +0200

Introduction

Hello World! This is my new GitLab page powered by Hugo. I’m setting up this blog to practise my math, foreign languages and IT skills.

Why Hugo?

My original goal is to set up a personal blog for posting math.

I used to work with Octopress, but resolving the dependencies and other technical issues had actually took much more time and effort than expected. As a result, I digressed a lot from my studies to look into those problems.

Math Sample

Sun, 05 Mar 2017 00:00:00 +0000

This is a sample created by the developer of Beautiful Hugo.

KaTeX can be used to generate complex math formulas server-side.

$$ \phi = \frac{(1+\sqrt{5})}{2} = 1.6180339887\cdots $$

Additional details can be found on GitHub or on the Wiki.

Code Sample

Tue, 08 Mar 2016 00:00:00 +0000

This is a sample created by the developer of Beautiful Hugo.

The following are two code samples using syntax highlighting.

Mon, 01 Jan 0001 00:00:00 +0000

j— title: “Import Once in Julia” date: 2021-08-23T16:24:40+02:00 categories:

technical support tags:
julia draft: false

Background

I’m reading Think Julia to repick the language again.

To import a package/module, we using Foo.
To run a script within the REPL, we include("foo.jl").

This is useful for user-defined functions, which are usually multi-line.

Problem

How to avoid importing a module/including a file twice?

Solution

Here’s a modified code from the book to give an example.

Java

Mon, 01 Jan 0001 00:00:00 +0000

Je me sers de ce fichier comme

la speech pour mes futurs entretiens
le dépôt des doutes et leurs réponses que je recueilis

dans mon apprentissage. Je ne cherche pas une réponse détaillée (qu’on trouve facilement dans un livre ou un manuel).

Générale

C’est quoi Java ?

Java est un langage de programmation intermédiaire.
- compilé : son compilateur produit un fichier qui n’est ni visible pour le développeur ni pour le système d’exploitation.
- interprété : le fichier compilé
  - en bytecode Java avec l’extension CLASS, ou
  - en archive JAR doit être interprété par une machine virtuelle.
Pourquoi utiliser Java ?

Questions Réponses

Mon, 01 Jan 0001 00:00:00 +0000

Une question ? Une réponse.

Java

Solarized Sublime Sekai

Optimisation d'une VM GCP et domptage de Neovim

1. Transfert de fichiers avec rsync

Rust Project Structure for rust-canto

Background

Five lessons learnt from chat bot

1. Avoid the “Crates.io Path Dependency” Trap

Typst Package for Jyutcitzi

Background

A soft “introduction” to “Introduction to Jyutcitzi”

Imprimante HP Deskjet 4100 sous Linux

Introduction

Choisir La Stabilite en Christ

Plus grande chute du plus grand royaume

Dix Pensees Formidables Chretiennes

Tikz Loop Over Coordinates

Background

Problem

Inspiration

Upgraded to Hugo v0.135

Background

Problem

Exponential Function Series Definition

Motivation

Solution

Start Oracle From Git Bash

Goal

Assumption

Problem

Solution

Closer Look into ArrayList Iterator

Background

Problem

Discussion

Notes du Jour

Passed Codingame Java Certification Test

String regex replace using capture groups

Check characters properties using Character’s static methods

Notes pour l'algo des tableaux

Notes d'algo du jour

Diapo Sur HashMap

Visual Studio Code

Usual keys

Navigation

Searching / Replacing

Fixed Archetype Error for This Site

Background

Problem

IntelliJ

Navigation

Searching / Replacing

Editing / Selection

Exploration of My First IntelliJ Project

Reuse Commands with Shell Arguments

Background

Finding Pandoc Logo

Background

Problem

Simple Document Templates

To get started

Some Public APIs to Be Viewed

Merge Two PDF to Single Encrypted PDF

Problem

My try

Solution

How to Start an Online Empire Without a Job

Difficulty

Solution

Ten Probably Handy Sites

Encrypt PDF on Command Line

Background

Problem

Adjust Git Bash Font and Window Size

Goal

Solution

Fujitsu LH532 Thermal Paste Application

Background

Photos

thermal paste on CPU displaced after ten years

thermal paste on fan displaced after ten years

Check characters properties using `Character`’s static methods