Self adjusting vertical line in scalar product

Question

I'm trying to define a new command for scalar product. So far, it looks like this:

\newcommand{\ilskal}[2]{\left(#1\left|#2\right)}

However, when I was trying to put something riddiculously high in one of the fields, the separator (|) remained the same height. I tried modifying the command:

\newcommand{\ilskal}[2]{\left(#1\left|\phantom{\right}#2\right)} 

However, that doesn't work; by putting a matrix in one of the fields I get an error. Putting anything else produces an error as well. Why? I tried substituting | for other vertical lines, but it didn't help.

Answer 1

You can use \middle:

\documentclass[a4paper]{article}
\usepackage{amsmath}

\newcommand{\ilskal}[2]{\left(#1\,\middle\vert\,#2\right)}

\begin{document}

\[
\ilskal{\frac{2}{3}}{\frac{5}{7}}
\]

\end{document}

Here's the definition using the mathtools package:

\documentclass[a4paper]{article}
\usepackage{mathtools}

\DeclarePairedDelimiterX{\ilskal}[2]{(}{)}{#1\,\delimsize\vert\,#2}


\begin{document}

\[
\ilskal*{\frac{2}{3}}{\frac{5}{7}}
\]

\end{document}