Custom Macros

If you find yourself typing the exact same complex block of LaTeX code repeatedly, you can create a custom macro using the \newcommand directive. This allows you to define your own commands.

Basic Macros (Shorthand)

The simplest use of a macro is to create a shorthand for a long command. You define macros in the preamble (before \begin{document}).

% Define the macro in the preamble
\newcommand{\R}{\mathbb{R}}
 
\begin{document}
  % Use the macro in the text
  Let $x \in \R$.
\end{document}

In this example, every time the compiler sees \R, it replaces it with \mathbb{R}.

Macros with Arguments

You can make your macros dynamic by allowing them to accept arguments. You specify the number of arguments in square brackets [n], and reference them inside the definition using #1, #2, etc.

% Define a macro that takes 2 arguments
\newcommand{\vector}[2]{\begin{pmatrix} #1 \\ #2 \end{pmatrix}}
 
\begin{document}
  % Use the macro
  The vector is $\vector{x}{y}$.
\end{document}

This significantly reduces the amount of typing required for repetitive mathematical structures.

Redefining Existing Commands

LaTeX will throw an error if you try to use \newcommand to define a command that already exists.

If you explicitly want to overwrite a built-in LaTeX command, you must use \renewcommand.

% Change the default bullet point in itemize to a dash
\renewcommand{\labelitemi}{$-$}

Creating Custom Environments

Just as you can define custom commands, you can define custom environments (like \begin{myenv} ... \end{myenv}) using the \newenvironment directive.

This requires two code blocks: one for the code that should execute at the \begin statement, and one for the code at the \end statement.

% \newenvironment{name}{begin code}{end code}
\newenvironment{warningbox}
{
  \begin{center}
  \bfseries \color{red} WARNING: 
}
{
  \end{center}
}
 
\begin{document}
  \begin{warningbox}
    Do not touch the red button.
  \end{warningbox}
\end{document}