Making Multiline Equations

Just a quick post, as this is something that I've had to do (yet again), so I thought I'd write it down. When you need an equation with multiple lines, say when you're decomposing an equation through several steps, the procedure you should use is eqnarray:

Equation array: eqnarray
usage: \begin{eqnarray} ... \end{eqnarray}

The usage of eqnarray is fairly straight-forward: an equation array is a standard array with three columns formatted to the right, center and to the left {rcl}. The idea is that the left side of the equation is the first statement, the middle column is the = sign and the right column is the derivation. It differs from a standard array in that it is in the formula environment (within the $ environment) so it can take standard mathematical notation. The following example produces a two-line equation:

\begin{eqnarray*}
\Delta D(s,N) & = & D_N(\hat{\mu};,y) - D_{N_L,N_R}(\hat{\mu}_L,\hat{\mu}_R;y)\\
& = & \sum_{i=1}^n D(\hat{\mu};y_i) - \left[\sum_{i=1}^{n_L} D(\hat{\mu};y_i)+\sum_{i=1}^{n_R} D(\hat{\mu};y_i)\right]\\
\end{eqnarray*}

This produces the following equation:

\bar vs. \overline

Another quick post, this time about math. In particular about the \bar option. As many Latex users are aware, the \bar option is used to put a line over a letter/number in math mode, usually representing a mean. The problem with this method is that it puts a fixed-width bar over the letter (I think it's an underscore character '_') instead of covering the width of the letter(s).

This can be easily overcome with the overline option.

overline: \overline
usage: \overline{test}
Explanation: The overline option should be used instead of bar option.

The following code demonstrates the difference

\documentclass[12pt]{beamer}
\mode{
\usetheme{Boadilla}
}
\begin{document}
\begin{frame}[plain]
\begin{alertblock}{WRONG}
\begin{align*}
Z& = \frac{\bar{BMI}-\mu}{\sqrt{\frac{\sigma^2}{N}}} \\
& = \frac{\bar{BMI}-\mu}{SE(\bar{BMI})} \\
\end{align*}
\end{alertblock}
\begin{exampleblock}{RIGHT}
\begin{align*}
Z& = \frac{\overline{BMI}-\mu}{\sqrt{\frac{\sigma^2}{N}}} \\
& = \frac{\overline{BMI}-\mu}{SE(\overline{BMI})} \\
\end{align*}
\end{exampleblock}
\end{frame}
\end{document}

Which produces the following slide

Formatting Tables

I suppose I should start with the subject that made me start this blog in the first place: formatting tables. Now I'm sure this is the first in a series of posts on tables, as anyone who has worked with them knows how finicky they can be.

The two aspects of tables I'm explaining today are the column and row separation values. For those that are looking for quick fixes, I'll give them to you right away:

Column Width: \tabcolsep
Usage: \renewcommand\tabcolsep{6pt}
Explanation: tabcolsep is HALF the space between two columns. Default value is 6pt

Row Height: \arraystretch
Usage: \renewcommand\arraystretch{1}
Explanation: arraystretch is a FACTOR representing the distance between two rows. Default is 1

The two variables are manipulated in different ways: tablecolsep is a unit, so it can be specified in a variety of ways (pt, ex, em, etc...) which arraystretch is a factor, so it has no units.

The code demonstrates how to manipulate the variables, using beamer slides.

\documentclass{beamer}
\begin{document}
\begin{frame}[fragile]
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|c|c|c|c|c|}\hline
1 & 2 &3 &4 &5 &6 &7 &8 &9 & a &b &c &d &e &f \\\hline
Wide Column & & & & & & & & & & & & & & \\\hline
\end{tabular}
\renewcommand\arraystretch{1.1}
\renewcommand\tabcolsep{3pt}
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|c|c|c|c|c|}\hline
1 & 2 &3 &4 &5 &6 &7 &8 &9 & a &b &c &d &e &f \\\hline
Wide Column & & & & & & & & & & & & & & \\\hline
\end{tabular}
\renewcommand\arraystretch{0}
\renewcommand\tabcolsep{0pt}
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|c|c|c|c|c|}\hline
1 & 2 &3 &4 &5 &6 &7 &8 &9 & a &b &c &d &e &f \\\hline
Wide Column & & & & & & & & & & & & & & \\\hline
\end{tabular}
\renewcommand\arraystretch{2}
\renewcommand\tabcolsep{6pt}
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|c|c|c|c|c|}\hline
1 & 2 &3 &4 &5 &6 &7 &8 &9 & a &b &c &d &e &f \\\hline
Wide Column & & & & & & & & & & & & & & \\\hline
\end{tabular}
\end{frame}
\end{document}

Which produces these slides