Custom Commands

LaTeX allows you to define your own commands to simplify complex tasks or enforce consistency.

Defining a New Command

Use \newcommand to create a new command. This is useful for abbreviations or commonly used phrases.

\newcommand{\R}{\mathbb{R}} % New command "R"
The real numbers are denoted by $\R$.

Adding Arguments

You can create commands that take arguments. The number of arguments is specified in [] (up to 9). Use #1, #2, etc. to refer to them.

\newcommand{\boldtext}[1]{\textbf{#1}}

This is \boldtext{important}.

Example: Complex Math Command

Instead of typing \frac{\partial f}{\partial x} repeatedly:

\newcommand{\pd}[2]{\frac{\partial #1}{\partial #2}}

The derivative is $\pd{f}{x}$.

Optional Arguments

The first argument can be optional.

\newcommand{\plusbinomial}[3][2]{(#2 + #3)^#1}

Default (power 2): $\plusbinomial{x}{y}$ % (x+y)^2
Power 3:           $\plusbinomial[3]{x}{y}$ % (x+y)^3

Renewing Commands (\renewcommand)

If a command already exists (like \emph or \section), use \renewcommand to change its definition.

\renewcommand{\abstractname}{Executive Summary}

Defining Environments

Use \newenvironment{name}{begin code}{end code}.

\newenvironment{king}
    {\rule{1ex}{1ex}%
     \hspace{\stretch{1}}}
    {\hspace{\stretch{1}}%
     \rule{1ex}{1ex}}