redeclare math operator

Guenter Milde

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Nov 12, 2008, 9:11:56 AM11/12/08

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If I want to define a new math operator, I can use e.g.

\DeclareMathOperator{\sgn}{sgn}

however, if I want to re-define an existing math operator (e.g. the real
part of a complex number with Re in roman face according to ISO 31), I
have to realise that the command

\reDeclareMathOperator{\Re}{Re}

does not exist.

What is the recommended method in this case?

Günter

Werner Grundlingh

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Nov 12, 2008, 10:30:40 AM11/12/08

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Here's an attempt at getting around your 'problem':

\documentclass{article}

\usepackage{amsmath}

\DeclareMathOperator{\newRe}{Re}

\begin{document}

$\Re \ell$

\let\Re=\newRe

$\Re \ell$

\end{document}

Werner

Mariano Suárez-Alvarez

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Nov 12, 2008, 10:51:25 AM11/12/08

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I do not know if this is recommended, but one way
to do this is to `undefine' \Re:

\documentclass{article}
\usepackage{amsmath}
\let\Re\undefined
\DeclareMathOperator{\Re}{Re}
\begin{document}
$\Re z$
\end{document}

-- m

Lars Madsen

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Nov 12, 2008, 1:50:00 PM11/12/08

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\renewcommand\Re{\opratorname{Re}}

hmm, might be an idea to a a \reDeclareMathOperator to mathtools

--

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Dan Luecking

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Nov 12, 2008, 2:58:59 PM11/12/08

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On 12 Nov 2008 14:11:56 GMT, Guenter Milde <mi...@users.berlios.de>
wrote:

>If I want to define a new math operator, I can use e.g.
>
> \DeclareMathOperator{\sgn}{sgn}
>
>however, if I want to re-define an existing math operator (e.g. the real
>part of a complex number with Re in roman face according to ISO 31), I
>have to realise that the command
>
> \reDeclareMathOperator{\Re}{Re}
>
>does not exist.

\renewcommand{\Re}{\operatorname{Re}}

The difference between defining a command to be
\operatorname{something} and defining it by
\DeclareMathOperator, is one level of macro
expansion. With the above definitions,
\Re --> operatorname{Re}
--> [internal code for \operatorname{Re}]
\sgn --> [internal code for \operatorname{sgn}]

This is documented (amsldoc.pdf section 5, page 14).

Dan
To reply by email, change LookInSig to luecking

Guenter Milde

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Nov 13, 2008, 7:04:19 AM11/13/08

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Lars Madsen <dal...@RTFSIGNATUREimf.au.dk> schrieb:

> Guenter Milde wrote:
>> If I want to define a new math operator, I can use e.g.

>> \DeclareMathOperator{\sgn}{sgn}

>> however, if I want to re-define an existing math operator

...

>> \reDeclareMathOperator{\Re}{Re}
>> does not exist.

> \renewcommand\Re{\operatorname{Re}}

> hmm, might be an idea to add a \reDeclareMathOperator to mathtools

After looking at clsguide.pdf, I'd recommend \ReDeclareMathOperator as name.

Looking at the other replies, I would suggest something like

\newcommand{\ReDeclareMathOperator}[1]{
\let \csname #1\endcsname \undefined
\DeclareMathOperator{\csname #1\endcsname}{#1}
}

Thanks to all posters,

Günter

Robin Fairbairns

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Nov 13, 2008, 7:42:35 AM11/13/08

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Guenter Milde <mi...@users.berlios.de> writes:
>Looking at the other replies, I would suggest something like
>
>\newcommand{\ReDeclareMathOperator}[1]{
> \let \csname #1\endcsname \undefined
> \DeclareMathOperator{\csname #1\endcsname}{#1}
>}

\newcommand{\ReDeclareMathOperator}[1]{%
\expandafter\let \csname #1\endcsname \undefined
\DeclareMathOperator{\csname #1\endcsname}%
}

would be a better bet. (note the comment marks. probably not really
necessary since the command is generally used in the preamble, but
good practice nevertheless.)
--
Robin Fairbairns, Cambridge

Donald Arseneau

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Nov 13, 2008, 7:07:22 PM11/13/08

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On Nov 12, 6:11 am, Guenter Milde <mi...@users.berlios.de> wrote:

> however, if I want to re-define an existing math operator [but]

>
> \reDeclareMathOperator{\Re}{Re}
>
> does not exist.

Hold on. The command is "DeclareMathOperator", not
"NewMathOperator". It should not require a previously-undefined
command name, but should work like \DeclareRobustCommand.
File a bug report. (Fat chance it will change though.)

Donald Arseneau as...@triumf.ca

Dan Luecking

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Nov 14, 2008, 3:47:07 PM11/14/08

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amsopn.sty actually *uses* \DeclareRobustCommand, but
explicitly checks with \@ifdefinable before doing so.
One need only remove that (from the definition of
\@declmathop).

Alternatively, mathtools (or some package that implements
this) should use the new/renew naming system.

Personally, I always use \re and \im instead of \Re
and \Im. Easier to type, doesn't invoke this error,
and leaves the originals available. I'm a comlex
analyst and have to type them a *lot*.

Lars Madsen

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Nov 14, 2008, 5:53:49 PM11/14/08

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I'll keep following this thread to see what you guys end up
recommending, then I'll add that to mathtolls.

/daleif