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Re: Question on ComplexExpand

  • To: mathgroup at
  • Subject: [mg51137] Re: [mg51129] Question on ComplexExpand
  • From: Andrzej Kozlowski <akoz at>
  • Date: Wed, 6 Oct 2004 04:34:09 -0400 (EDT)
  • References: <>
  • Sender: owner-wri-mathgroup at

On 5 Oct 2004, at 17:37, Carlos Felippa wrote:

> *This message was transferred with a trial version of CommuniGate(tm) 
> Pro*
> This question is related to a previous post, and to a project in
> stability of a G&C feedback system I am working on.
> Is there a way to get ComplexExpand to automatically convert Abs to
> Sqrt,  Arg to ArcTan, etc., as target functions?    For example
>              ComplexExpand[Abs[x+y*I]]   gives  Sqrt[x^2+y^2]
>              ComplexExpand[Arg[x+y*I]]   gives  ArcTan[y/x]
> (Note: ComplexExpand assumes all symbols are real by default.)
> I wasnt able to find an option to do that in 4.2.1.  Thanks.

ComplexExpand[Abs[x + y*I], TargetFunctions -> {Re, Im}]

Sqrt[x^2 + y^2]

ComplexExpand[Arg[x + y*I], TargetFunctions -> {Re, Im}]

ArcTan[x, y]

Andrzej Kozlowski
Chiba, Japan

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