The following code
\documentclass{scrartcl}
\usepackage{mathtools}
\DeclarePairedDelimiterX\innerp[2]{\left(}{\right)}{#1 \delimsize\vert \mathopen{}#2}
\DeclarePairedDelimiterX{\dualp}[2]{\langle}{\rangle}{#1\, , \mathopen{}#2}
\begin{document}
%
\[
\innerp{a}{b}
\]
%
%
\[
\dualp{a}{b}
\]
%
\end{document}
Gives the following error code:
./mwe.tex:8: Missing { inserted.
<to be read again>
\left
l.8 \innerp{a}{b}
I have just replaced the \langle by \left( and the \rangle by \right) . So I am wondering what is wrong.
\leftand\rightare wrong. Just use(and). – campa May 03 '21 at 11:59\left/righthas no relevancy here as they are applied automatically via\innerp*. Tip if you use\delimsize\lvertinstead, then you don't need the\mathopen. – daleif May 03 '21 at 12:26{\left(}... has ever worked it would have been a very long time ago. I do not recall it ever being a supported feature. – daleif May 03 '21 at 12:45