Use of mathtools

Question

I have defined the \absas described in the Mathtools Users Guide 3.6. But I would like to habe the stared-version as default (=\abs). I looked further and found on 3..6.1 (as I thought) a way to do this. But I failed: Changing {star} and {nostar} doesn't make any difference. Am I wrong with my thinking?

\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage{mathtools}
% Example from Mathtools-Manual 3.6.1
%\DeclarePairedDelimiter\abs\lvert\rvert
%   \reDeclarePairedDelimiterInnerWrapper{\abs}{star}{#1#2#3}
%   \reDeclarePairedDelimiterInnerWrapper{\abs}{nostar}{\mathinner{#1#2#3}}
% MY try:
\DeclarePairedDelimiter\abs\lvert\rvert
    \reDeclarePairedDelimiterInnerWrapper{\abs}{nostar}{#1#2#3}
    \reDeclarePairedDelimiterInnerWrapper{\abs}{star}{\mathinner{#1#2#3}}
%
\begin{document}
%
\[
    \abs{\frac{\pi}{2}} \quad  \quad \abs*{\frac{\pi}{2}} 
\]
%
\end{document}

Did you see the posting Swap definition of starred and non-starred command? — Mico, Aug 31 '16 at 13:37
Trust me: you don't want to use automatic sizing by default. — egreg, Aug 31 '16 at 13:43
@ Mico, no, but now. Thanks for the link. @egreg: can you explain this to me? — Ulrich, Aug 31 '16 at 14:25
@Ulrich Most of the times, the automatic sizing chooses too big fences than necessary. — egreg, Aug 31 '16 at 14:57
@egrep: i.e. \abs{x} is ok but \abs*{x} maybe wrong (I guess you have a better example)? So your recommondation is to use use the stared-version only in displayed math environments? — Ulrich, Aug 31 '16 at 15:17
@Ulrich not there I'd also use the normal one or manual scalled. Use only auto scale when you really need it. \abs*{\sum_i} does not look very good, the fences are too big. There are many other examples. Once you have edited enough manuscripts you'll know the hazards of auto scaling. — daleif, Aug 31 '16 at 20:26

Use of mathtools

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