After having used LaTeX as my primary document creation tool for a few years now, I’ve amassed some tricks into my veritable arsenal of computer geekery. I thought I’d spill the beans on one of them today.

Creating Your Own Macros

Once upon a time, you had a document for which you needed some mathematical expression that repeated way too many times. You hated typing it, and you felt the carpal tunnel settling in[0]. Well, LaTeX feels your pain, and wants to help out.

In one such homework last semester, I found myself typing something like this same sequence over and over again: 

\[ \left( egin{array}{c} n \ p \end{array} 
ight) \]

Not that bad? Try typing it out 10 times[1]. It was tedious, and made the code entirely unreadable.

How can LaTeX help out? With the ability to define your own commands. We can take that code above, and put the following definition into the preamble (before the egin{document}) of your LaTeX document: 


ewcommand{
pchoose}[2]{
    \left( egin{array}{c} #1 \ #2 \end{array} 
ight)
}

What’s going on here? Well, the ewcommand command tells LaTeX that you’re going to be defining a new macro. The first argument is the name that you’re going to use for this macro (include the prefix slash, and it can’t be an existing keyword, such as egin). The second argument, in brackets, is the number of arguments to your new macro. In the example above I have two arguments: one for the top variable and one for the bottom one. Lastly, you tell LaTeX what the code for the macro is. Notice that I use the variables #1 and #2 where I want the macro to put whatever variables are passed to it[2].

Now you can change that entire math expression above to simply: 

\[ 
pchoose{n}{p} \]

How does this break down? Notice that we use the command pchoose because that’s the name that we gave to the macro. Then we simply list the arguments in order. Note that each argument gets its own curly brackets. LaTeX will replace the variables #1 and #2 with these arguments that we pass it. It will replace them in order – n gets passed to #1, etc.

Dead simple. You can do this with any expression. It doesn’t need to be in math mode.

A Step Further: Your Own Package

This is all good, but what if you have a command that you want to use on two different LaTeX files? In the example above, I wanted to use that command for every homework file I created in that class. Sure, I could have just copied the command into every file I made, but that’s hack. What if I had an entire set of macros that I wanted to use? There’s an elegant solution, as always. And it involves creating your own package.

At its most basic level, a LaTeX package is just a file with a bunch of macros defined in it. Well, we already know how to make a macro (see above), and hopefully we already know how to make a file. We should be set.

To make a package called mymacros, create a file called mymacros.sty, and keep it in the directory of the LaTeX file that uses it. In my class example, I would have created a file called ece310.sty that looked like this: 

% New command definition

ewcommand{
pchoose}[2]{
    \left( egin{array}{c} #1 \ #2 \end{array} 
ight)
}

and at the top of my homework files I would have had the line: 

    \usepackage{ece310}

Done. That’s LaTeX macros in a nutshell. Nothing confusing about them, and they can really help out and make your documents easier all around.

[0] Switch to Dvorak and save your wrists. Bask in your glowing aura of l33t.

[1] I can already hear the vim/emacs users deriding my lack of copy/paste macro skills. Well, the entire point of this post is to showcase LaTeX macros.

[2] For bonus points check out this page on macros, specifically the part about default parameters. Now, that’s neat.