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MathGroup Archive 2004

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Re: A way around the limitations of Re[] and Im[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51136] Re: A way around the limitations of Re[] and Im[]
  • From: pein <petsie at arcor.de>
  • Date: Wed, 6 Oct 2004 04:34:08 -0400 (EDT)
  • References: <cjr8lg$opp$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Carlos Felippa schrieb:

> As you know, Re[expr] and Im[expr] are left unevaluated when expr is
> not numeric.  I had good luck in simple cases with the following
> substitution trick:
>   
>         Real[c_]:=c/.I->0;     Imag[c_]:=(c-Real[c])/.I->1;
> 
> Do you see any problem with these definitions?
> 
Yes.
The very simple example Sqrt[a] fails with your definitions.
ComplexExpand[Sqrt[a], TargetFunctions -> {Re, Im}] gives a correct result.

-- 
Peter Pein, Berlin


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