Vrftjkry

I'm trying to make a new command for something like this:

operatorname{Re}leftlbracenum{1+2i}rightrbrace

Because I'm using the mathtools package already I tried to do something like this:
(And I have to undefine the previous Re and Im commands, because they are ugly and this command should be obviously called Re and Im.)

letReundefined

letImundefined

DeclarePairedDelimiterRe{operatorname{Re}lbrace}{rbrace}

DeclarePairedDelimiterIm{operatorname{Im}lbrace}{rbrace}

This will work, but will also spit put many errors. Like: Missing { inserted. end{align} and so on.

Then I thought: Yes, this is probably, because the font can not scale (and shouldn't), like the lbrace and rbrace. And I tried something like this:

letReundefined

letImundefined

DeclarePairedDelimiterbraces{lbrace}{rbrace}

newcommand{Re}{1}{operatorname{Re}braces*{#1}}

newcommand{Im}{1}{operatorname{Im}braces*{#1}}

But this will produce:

Missing $ inserted. newcommand{Re}{1}{operatorname{Re}

Missing begin{document}. newcommand{Re}{1}{operatorname{Re}

Inserting ensuremath or something like that doesn't help much.

Last try:

letReundefined

letImundefined

newcommand{Re}{1}{operatorname{Re}leftlbrace #1 rightrbrace}

newcommand{Im}{1}{operatorname{Im}leftlbrace #1 rightrbrace}

Missing $ inserted. newcommand{Re}{1}{operatorname{Re}

Missing begin{document}. newcommand{Re}{1}{operatorname{Re}

You can't use `macro parameter character #' in math mode. ...nd{Re}{1}{operatorname{Re}leftlbrace #

It can't be this hard to make something like this work, or can it? I really don't know what I should try next, or what am I even doing wrong.

You have the incorrect syntax for newcommand.

newcommand{Re}{1}

should be

newcommand{Re}[1]

You can use the DeclarePairedDelimiterXPPfrom mathtools. It will define Reand Im commands, which have a star version (adds a pair of implicit left right in front of the delimiters), but they also accept an optional argument among big, Big, bigg and Bigg, which adds a pair oof implicit bigl bigr, &c.

documentclass[10pt]{article}

usepackage{mathtools} %

letReundefined

letImundefined

 DeclarePairedDelimiterXPPRe[1]{operatorname{Re}}{lbrace}{rbrace}{}{#1}

 DeclarePairedDelimiterXPPIm[1]{operatorname{Im}}{lbrace}{rbrace}{}{#1}



begin{document}



   [ Re*{frac{z-1}{z + 1}}qquad Im[Big]{frac{z-1}{z + 1}} ]%



end{document}