Here’s an example illustration made with Jpgfdraw following a drawing in Singer/Thorpe Lecture Notes in Elementary Topology and Geometry, I made freehand it to illustrate homotopy of paths in my notes.

Screenshot:

Output in pdf format: homotopy.pdf
Jpgfdraw binary file: homotopy.jdr
exported tex file: homotopy.tex

LaTeX main document:

\documentclass[a4paper,10pt]{article}
\usepackage[landscape]{geometry}
\usepackage{amsmath,pgf}
\pagestyle{empty}
\begin{document}
\centering
\input{homotopy}
\end{document}

On June 13 2008 jtin informed in the LaTeX Community Forum that he started a new webservice: mathurl.com. This site turns standard LaTeX input with amsmath extensions into png images that can be embedded other websites. Permanent links to LaTeX expression and output bitmap are created and can be used inside emails or on websites for the exchange of formulas.

The entries of matrix columns are centered by default. Let’s see an example:

\[
  \begin{pmatrix}
    1 &  2 &  1 \\
    0 & -2 & -3 \\
    0 & 3 &  -2
  \end{pmatrix}
\]

Output:

For right alignment you could use an array environment instead of pmatrix. I will show a possibility to get left, right or centered alignment by redefining the internal amsmath macro \env@matrix. Its original definition in version 2.13 is:

\def\env@matrix{\hskip -\arraycolsep
  \let\@ifnextchar\new@ifnextchar
  \array{*\c@MaxMatrixCols c}}

I introduce an optional parameter, its default value is c:

\makeatletter
\renewcommand*\env@matrix[1][c]{\hskip -\arraycolsep
  \let\@ifnextchar\new@ifnextchar
  \array{*\c@MaxMatrixCols #1}}
\makeatother

Now, if you write \begin{pmatrix}[r] … above you will get:

See complete source code example.

This topic was discussed in the Matheplanet Forum.

There’s a lot of freely available documentation for LaTeX, but there’s a pitfall: some documents that are still online are outdated and therefore contain obsolete information. Documents like “Obsolete packages and commands” (”l2tabu”) address the need of up-to-date information.

For instance the obsolete eqnarray environment frequently appears in questions of new LaTeX users and many people including me usually answer: don’t use eqnarray and give advice how to use the align environment of amsmath instead.

Here’s a summary of the problems with eqnarray:

• the spacing around relation symbols are inconsistent,
• long equations might collide with the equation numbers,
• there could be problems with labels and references.

Here is one small example document just to illustrate the space inconsistany problem:

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath}
\begin{document}
\begin{minipage}{0.5\textwidth}
equation:
\begin{equation*}
  z_0 = d = 0
\end{equation*}
\begin{equation*}
  z_{n+1} = z_n^2+c
\end{equation*}
align:
\begin{align*}
  z_0 &= d = 0 \\
  z_{n+1} &= z_n^2+c
\end{align*}
eqnarray:
\begin{eqnarray*}
  z_0 &=& d = 0 \\
  z_{n+1} &=& z_n^2+c
\end{eqnarray*}
\end{minipage}
\end{document}

Compile for yourself and examine it, if you want. For a quick look here’s a screenshot of the output:

Notice the difference of the spacing around the equal sign in the eqnarray environment compared to equation and even compared to the other equal sign inside the first eqnarray line.
If you try to repair the spacing by adjusting \arraycolsep you will notice that all other arrays including matrices will be affected too. So the best solution is to use amsmath, this package provides even more environments useful for multiline formulas and a lot more enhancement for mathematical typesetting.

See the amsmath user’s guide.

For further information regarding this topic you may have a look at the article “Avoid eqnarray!” by Lars Madsen published in the PracTeX Journal 4 2006.

This topic was discussed on MatheBoard.