General ⇒ if, else, fi

[x42bn6]

Probably because they're such common terms, I can't find anything explaining how to get conditionals to work.

I have the following bit of code:

Code: Select all

\DeclareMathOperator{\fisherInformationOp}{\operatorname{I}}
\newcommand{\I}[2][]{\fisherInformationOp_#1\left(#2\right)}

The idea being that sometimes I want to subscript things but not all the time.

However, when there is only one argument, the subscript takes the token \left and won't compile as there's no partnering \right. So I want to do something like:

Code: Select all

\DeclareMathOperator{\fisherInformationOp}{\operatorname{I}}
\newcommand{\I}[2][]{
	% If there are two arguments then...
		\fisherInformationOp_#1\left(#2\right)
	% Otherwise...
		\fisherInformationOp\left(#2\right)
	% \fi
}

How would I fill in the comments?

[localghost]

Code: Select all

\documentclass[11pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}

\DeclareMathOperator{\op}{Op}
\newcommand{\opind}[2][\relax]{\op_{#1}\left(#2\right)}

\begin{document}
  $\opind{x} \opind[1]{x}$
\end{document}

Best regards
Thorsten

[x42bn6]

That works, thanks.

Just out curiosity, could I know:

- What \relax does?
- Any sort of documentation on \if, \ifx, \else, \fi and so on?

[localghost]

[...] What \relax does? [...]

Nothing (just relax).

[...] Any sort of documentation on \if, \ifx, \else, \fi and so on?

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