macros
I would like to define a new command with two optional arguments, one at the end. This works:
\newcommand{\matr}[3]{{}_{#1}\textbf{#2}_{#3}}
\matr{b}{M}{e}
But I would like to call it like this:
\matr[b]{M}[e]
leaving out the optional brackets, if I don't need them. Is it possible?
You could use the xparse package which offers great possibilities for defining user commands:
My First attempt:
\usepackage{xparse}
\DeclareDocumentCommand{\mymat}{o m o}
{%
\IfNoValueTF{#1}
{\IfNoValueTF{#3}{\mathbf{#2}}{\mathbf{#2}^{#3}}}
{\IfNoValueTF{#3}{\mathbf{#2}_{#1}}{\mathbf{#2}_{#1}^{#3}}}
}
Egregs simpler solution with IfValueT
\usepackage{xparse}
\DeclareDocumentCommand{\mymat}{o m o}
{%
\mathbf{#2}\IfValueT{#1}{_{#1}}\IfValueT{#3}{^{#3}}
}
m stands for mandatory argument, o for optional.
IfValueT{argument}{true code} checks if the argument was given and calls either true code or does nothing.
IfNoValueTF{argument}{true code}{false code} checks if the argument was not given and calls either {true code} or {false code}
Result (You should maybe add a negative math space \! if you have an A matrix.:
\mymat{A}[\!\top]):
\begin{document}
\begin{equation}
\mymat{A}
\mymat[1]{A}
\mymat{A}[\top]
\mymat[1]{A}[\top]
\end{equation}
\end{document}
If you'd like a command where you can pass a single argument as a comma-separated list, rather than using \\ inside the argument (like Werner suggested), you could do the following:
\documentclass{article}
\usepackage{amsmath}
\usepackage{etoolbox} % needed for the \forcsvlist command
\newcommand*{\addrow}[1]{#1\\}
\newcommand{\m}[1]{%
\begin{bmatrix}
\forcsvlist\addrow{#1}%
\end{bmatrix}}
\begin{document}
\[
\m{1,2,3}
\]
\end{document}
Best Answer
You want to use
\NewDocumentCommand. Theoargument specifier means an optional argument with no default value, which can be tested with\IfValueTF(in this case only the “true“ branch is necessary).Note that
\textbfis wrong in this context and you want\mathbf.