LaTeX.org

Go to Document --> Settings --> Document Class: add enabledeprecatedfontcommands in the text field marked Custom.

Minimal might not be the right word, all you need to describe your problem is:

\documentclass{article}
\usepackage{tikz}
\definecolor{mainblue}{HTML}{0E5484}
\definecolor{maingray}{HTML}{B9B9B9}
\newcommand\skills[1]{
\renewcommand{\skills}{
\begin{tikzpicture}
\foreach [count=\i] \x/\y in {#1 ...

For example, to plot the first column versus the second and fourth columns, you can do as in the code below. The column count start at zero, hence x index=0. To plot different columns, just use different values for y index. The skip first n skips the first n lines of the file.

funclines3.png ...

goltoof, could you specify exactly how that file should be read? Is it just one column vs. another? I understand there are other forms of these files, with more complex formats, do you need to generalize to those?

The onehalfspacing environments have been added to individual paragraphs because, somehow, the paragraph settings has been changed. Seems the simplest way of removing it is to select all the text, right click -> Paragraph settings. Set Line spacing to Default if it isn't already, and click Apply ...

We really need more information. Which template is this, can you give a link?

I'm surprised you got any output at all. The \center command isn't really defined, as far as I know, though there is a center environment. But you don't need that, as stuff within equation is centered anyway, unless you specify otherwise. Further, as equation is a displayed math environment, there ...

If I understand correctly, yes you can add the same to your other enumerations. However, enumitem also allows you to set the style of all enumerations globally:
\setlist[enumerate,1]{label=\textbf{\arabic*}.}
Add this to your preamble, after loading enumitem. Then you can remove all the optional ...

Use the enumitem package instead:

\documentclass[12pt,fleqn,reqno]{article}
\usepackage{amsfonts,graphics,epsfig,cite}
\usepackage{amsmath,graphicx,amssymb,amsthm}
\usepackage{enumitem}

\begin{document}
\begin{enumerate}[label=\textbf{\arabic*}.]
\item Is $n$ even or $1 < \gcd(a,n) < n$?
\item ...

pgfplots can even use gnuplot to compute the coordinates.