Problem

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

Attempt

1. Logout: didn’t work at all
2. 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.

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.

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

1. Sed conditional match and execute command with offset, and
2. A question about AWK multiple line recognition.

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.

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.

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

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.

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

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:

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 $

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.

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