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## On \parskip

I must copy this answer from tex.se. It is really useful. I often change \parskip and always find the lists look awful.

The main reason why “playing with \parskip is a bad idea” is that this length also affects list environments. Quoting from Mittelbach (1989), With LateX into the Nineties, section 3.1 “Implementation desasters”:

The generic list environment is one of the central modules of the LaTeX implementation. It is used internally by most standard environments provided by LaTeX; even environments such as center are handled as a special kind of list […]

• An actual conceptual bug was the decision to add the value of \parskip to all vertical spacing parameters, even when it is used in places where no paragraph ends. This means that changing this parameter influences the layout in unexpected places, which in turn means that other parameters must be adjusted unnecessarily to compensate for this undesired side effect.

The last sentence describes what the parskip package, the options of the same name of theKOMA-script classes and the \abnormalparskip macro of the memoir class do: Besides setting \parskip to a positive value (and, with the exception of memoir, setting \parindentto zero), they adjust the spacing before and after lists.

Why does KOMA-scripthave so many options for parskip? You may choose between a vertical space equal to \baselineskip (full) or 0.5\baselineskip (half). You may also choose the minimum amount of whitespace to be left at the end of the last line of a paragraph (up to0.33\linewidth); such whitespace increases the perceptibility of the start of a new paragraph.

Regarding \parindent: As Ulrike has explained, changing this length is not a problem.

## Create standalone figures which are input-able

If you are using PGF/TikZ (or any drawing language for (La)TeX such as PSTricks), you will soon find yourself either:

• Re-compile an entire long LaTeX document just to see the effect of a small change you have made in a figure; or
• Maintain a simplified master LaTeX file for every figure file (that’s 2 files for each figure) so that you can compile the figure quickly; or
• Keep changing the preamble template for a tool like QtikZ to incorporate your custom definitions and packages for your figures.

Any of the above methods is cumbersome, time-consuming and inefficient. A much better way is to use the standalone package. For example, you are creating a figure in TikZ for your long paper. You put the figure code in a TeX file with a full preamble & the usual document environment, as if you are writing a small document with only one figure in it. But you don’t use the usual document class (e.g. article).  You use the class standalone instead, as follows:

% File myfigure.tex
\documentclass{standalone}
\usepackage{tikz}
\usepackage{mypackage}
\input{mydefs}
\begin{document}
\begin{tikzpicture}
\draw [color=red] (0,0) rectangle (2,1) node [midway] {Cool};
\end{tikzpicture}
\end{document}


If you compile this file, you will get the same result as if you used the preview package. You can make small changes and re-compile only the figure quickly.

In you main LaTeX file, you must use the standalone package at the very beginning of the preamble, and input the figure file as usual. For example:

\documentclass{article}
\usepackage{standalone}
\usepackage{tikz}
\usepackage{mypackage}
\input{mydefs}
\title{Test of the \texttt{standalone} package}
\begin{document}
\maketitle
This is a figure.
\begin{figure}
\centering
\input{subfile}
\caption{A figure.}
\end{figure}
\end{document}


You can compile this main file as usual. When being input, the preamble of the figure file (i.e. everything between \documentclass and \begin{document}) is skipped.

This method is more flexible and more convenient than the above methods. You maintain only one file per figure, and can edit and re-compile graphic code quickly.

## New command and conditioning

To create a new custom command in LaTeX, the command \newcommand is well-known. Its full usage is:

\newcommand{\commandname}[n][d]{definition}


where

• \commandname is the name of the new command, with backslash; this name must have never been defined.
• n is the number of arguments of the new command; if ignored, there will be no argument.
• d is the default value of the first argument; if not provided, the first argument will be required.
• definition is the definition of the new command.

If the command name has already been defined, the above command will cause an error. To re-define a command, use \renewcommand instead.

## Conditioning

In the definition of the new command (or in your LaTeX document in general), you may want to generate content differently based on certain conditions. For example, if the first argument of the command is empty, you want to do “this”, otherwise you want to do “that.” You can use standard TeX commands (TeX programming) for this task, but it is easier to use the package xifthen (an extended version of the package ifthen, you can also use the latter if you want). These packages define commands like


\ifthenelse{condition}{code if true}{code if false}



and commands for checking conditions, for example \isempty{} to check if something is empty.

As an example, the following command generates content differently based on its optional first argument:


\newcommand{\mycommand}[2][]{%

\ifthenelse{\isempty{#1}}%

{\ensuremath{{#2}_{\mathrm{on}}}}%

{\ensuremath{{#2}_{\mathrm{on}, {#1}}}}%

}



Usafe examples:

• \mycommand{f} produces $f_{\mathrm{on}}$
• \mycommand[i]{f} produces $f_{\mathrm{on}, i}$

## Typesetting numerical data (with units) in LaTeX

Typesetting numerical data (with units) in LaTeX correctly can be difficult and time-consuming. Note that I emphasized “correctly.”

Fortunately, siunitx comes to the rescue. From its description:

Typesetting values with units requires care to ensure that the combined mathematical meaning of the value plus unit combination is clear. In particular, the SI units system lays down a consistent set of units with rules on how they are to be used. However, different countries and publishers have differing conventions on the exact appearance of numbers (and units). A number of LaTeX packages have been developed to provide consistent application of the various rules: SIunits, sistyle, unitsdef and units are the leading examples. The numprint package provides a large number of number-related functions, while dcolumn and rccol provide tools for typesetting tabular numbers.

The siunitx package takes the best from the existing packages, and adds new features and a consistent interface. A number of new ideas have been incorporated, to fill gaps in the existing provision. The package also provides backward-compatibility with SIunits, sistyle, unitsdef and units. The aim is to have one package to handle all of the possible unit-related needs of LaTeX users.

Some examples stolen from its manual:

• \num{1+-2i} produces $1 \pm 2\text{i}$
• \num{.3e45} produces $0.3 \times 10^{45}$
• \si{kg.m.s^{-1}} or \si{\kilogram\metre\per\second} both produce $\text{kg}\,\text{m}\,\text{s}^{-1}$
• \si[per-mode=symbol]{\kilogram\metre\per\second} produces $\text{kg}\,\text{m} / \text{s}$

These are just a few examples. The possibility is much larger and the package is very useful. So keep my words: “Always use siunitx when possible.”

## Stack size limit error with hyperref

Today I got an weird error:

! TeX capacity exceeded, sorry [input stack size=1500].

The error text is not very helpful (not at all), but the compiler stopped at a section command of the form:

\section{Some text $\bm{d}$}

So I searched on Google and found the cause of the error. It was caused by hyperref trying to convert the mathematical expressions and symbols in the section title to a PDF link in the table of contents. Somehow hyperref does not like mathematical text in section titles, especially bold symbols. There are several solutions, but the following two are the easiest:

• Specify an alternative title for the section, usually called short title, and hyperref will use that for the link, like this:

\section[Some text d]{Some text $\bm{d}$}

• Specify pure text alternatives for the special symbols in the title, like this:

\section{Some text \texorpdfstring{$\bm{d}$}{d}}

Note that the same error can happen with not only mathematical symbols but also other special fonts, such as \verb (as some people reported).

References:

## Typesetting algorithms/pseudo-code

Two LaTeX packages are very popularly used to typeset algorithms/pseudo-code (actually one is a set of related packages). The first is the algorithms package and its related packages. The second is the algorithm2e package.

The algorithms package provides two basic environments: algorithm for creating floats that contain algorithms, and algorithmic for typesetting actual algorithms. It is very straightforward and easy to use, however it is not flexible and does not provide ways to customize the output easily. The algorithmicx package provides the same algorithmic environment, but with greater flexibility.

The algorithm2e package provides environments for typesetting algorithms with ultimate flexibility. By default, the output looks very much like actual code. It is very customizable. However, it is more difficult to use, and its syntax is not very intuitive.