# Make LaTeX easier with custom commands

LaTeX is a powerful tool for creating professional looking documents. Its ability to easily format mathematical equations, citations and complex figures makes LaTeX especially useful for developing peer-reviewed journal articles and scientific reports. LaTeX is highly customizable, which allows you to create documents that are not carbon copies of generic Microsoft Word templates.

Using LaTeX does have it’s drawbacks- instead of simply typing on a page, you construct the document by writing LaTeX code. Once you’ve written your code, a compiler translates it into a finished and formatted document. This can sometimes result in high overhead time for fixing bugs and managing format. But coding a document also has advantages, in addition to the vast array of existing LaTeX libraries and commands, you can create your own custom commands that speed up the writing and formatting process. Below I’ll overview the basics of creating custom LaTeX commands and provide some illustrative examples.

## Commands with no arguments

If you have an equation or a complex sequence of text that you know you’ll be repeating, you can create a custom command to produce it. For example, if I’m constantly referencing the equation for an Ordinary Least Squares (OLS) estimator, I can make a new command that produces it:

\newcommand{\OLS}{$\hat{\beta}=(X^TX)^{-1}X^Ty$}


There are three parts to defining this command, as shown in the figure below:

1. Tell LaTex you are defining a new command by specifying “\newcommand”
2. name the command (make sure to include the backslash)
3. Specify the output of the new command

Example LaTex code that calls the OLS command:

I can store complex terms using a predefined command: \OLS


Compiled output:

## Commands with basic arguments

### Single argument

You can also define commands that accept arguments. For example, if you want to make commands to assist tracking changes in a document, you can create a command that formats a section of added text so it has the color blue and is bolded:

\newcommand{\addtxt}[1]{{\color{blue} \textbf{#1}}} % Highlight text that has been added



The command defined above accepts one argument (shown as the “[1]”) and calls that argument using “#1”, as highlighted in the figure below:

Example Latex code using my command:

Demonstrating my custom commands with arguments:\addtxt{This text has be inserted into this sentence}


Example compiled output:

### Multiple arguments

You can also define commands with multiple arguments, for example, you can create a template sentence that provides an update the timing of a project:

\newcommand{\projReportA}[2]{The project was planned to finish on \textbf{#1}after reviewing current progress we have determined that it will likely finish on \textbf{#2}} % insert a date for when a project was planned to be completed and when a project is likely to be completed


Here, argument #1 is the date when the project was planned on being completed, and argument #2 is the date that the project will likely be completed.

Example use of this function:

Another way you can use an argument:\\ \\
\projReportA{September $9^{th}$}{October $1^{st}$}


Example compiled output:

## Commands with optional arguments

The project report command above can be modified to accept a default completion date with an option to include an updated date.

\newcommand{\progReportB}[2][September 9th]{The project was planned to finish on \textbf{#2}, after reviewing current progress, we have determined that it will likely finish on \textbf{#1}}


To create an optional argument, specify the default value of the first argument in a new set of brackets. Note that for basic Latex this only works for a single default argument, for more defaults you can use a package such as xparse.

Here’s an example using this new command with the default argument:

Here I'll will use the command without the optional argument, so it will print the default: \\
\\
\progReportB{September $9^{th}$}


This will compile to:

Here’s an example with the optional argument specified

Now I'll add the optional argument, which will be added in place of the default: \\ \\
\progReportB[October $1^{st}$]{September $9^{th}$}


This will compile to:

### Concluding thoughts

These simple examples only scratch the surface of what you can do with LaTex commands. I should also note that while custom commands are useful, LaTex also contains a large suite of packages with predefined commands that can be easily imported into your document.