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MathGroup Archive 1999

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Forcing Re[]'s to be Real

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18223] Forcing Re[]'s to be Real
  • From: afoglia at hal.physics.ucsb.edu (Anthony Foglia)
  • Date: Tue, 22 Jun 1999 20:41:15 -0400
  • Organization: University of California, Santa Barbara
  • Sender: owner-wri-mathgroup at wolfram.com

	I seem to have found an interesting problem involving computing the
real part of complex numbers.  (Interesting, in that it wasn't there a few
weeks ago when I ran the (as-far-as-i-can-remember) exact same code.)

I have a complex function:

k[w] := Sqrt[w^2 (1 + (2 / (1 + I w)))]

I want to graph the real and imaginary parts, but Mathematica doesn't want
to express the Re[k[w]] as a real number.  What do I mean?  Well, if I
type:

Re[Sqrt[1+I]]

I get out

Re[Sqrt[1+I]]

Same if I do Re[ComplexExpand[Sqrt[1+I]]], or Re[(1+I)^(1/2)].  But if I
enter:

Re[ComplexExpand[(1+I)^(1/2)]

Mathematica is kind enough to respond with:

2^(1/4) Cos[Pi/8]

I'm certain that this is the root of my problem, but I'll be damned if I
know why Mathematica doesn't like it now, but did a few weeks ago.  Any
help?

--Anthony 


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