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Re: ComplexExpand (V4.0)

• To: mathgroup at smc.vnet.net
• Subject: [mg20374] Re: ComplexExpand (V4.0)
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Sun, 17 Oct 1999 02:45:46 -0400
• References: <7u7rm9$p3h@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Blimbaum Jerry DLPC <BlimbaumJE at ncsc.navy.mil> wrote in message
news:7u7rm9$p3h at smc.vnet.net...
> Why does ComplexExpand[Re[1/(x + I y)]]   return
>
> x/Abs[x+ I y]^2
>
> rather then      x/(x^2+y^2)
>
> The Mathematica manual says that ComplexExpand assumes that the
> variables are real.
>
> thanks.   jerry blimbaum    NSWC  Panama City, Fl
>

Jerry,
The answer is correct under the assumption that x and y are real , but I'm
not sure why Absolute is allowed,
We do have

ComplexExpand[Re[1/(x + I y)], TargetFunctions -> {Re}]

    x/(x^2 + y^2)


Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565