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