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MathGroup Archive 1999

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Re: ComplexExpand (V4.0)

  • To: mathgroup at
  • Subject: [mg20374] Re: ComplexExpand (V4.0)
  • From: "Allan Hayes" <hay at>
  • Date: Sun, 17 Oct 1999 02:45:46 -0400
  • References: <7u7rm9$>
  • Sender: owner-wri-mathgroup at

Blimbaum Jerry DLPC <BlimbaumJE at> wrote in message
news:7u7rm9$p3h at
> 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

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 Hayes
Mathematica Training and Consulting
Leicester UK
hay at
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

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