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MathGroup Archive 2004

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Re: complex analysis problem in mathematica 3.0

  • To: mathgroup at smc.vnet.net
  • Subject: [mg48470] Re: complex analysis problem in mathematica 3.0
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Tue, 1 Jun 2004 03:02:46 -0400 (EDT)
  • Organization: The University of Western Australia
  • References: <c9ec75$g9q$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <c9ec75$g9q$1 at smc.vnet.net>,
 BranasMan <branasREmoVe at mail.inet.hr> wrote:

> i have a complex function:
> 
> H(s)=1 / (s^3 + 2s^2 + 2s + 1)
> 
> whan i replace "s" with j*w (j=sqrt(-1)) i get:
> 
> H=1 / (1 + j2w -2w^2 - jw^3)
> 
> i would like to get that function in shape of : 
> H=something + j*something_else i.e. the complex
> and real part apart.
> 
> i played with Re and Im,but it seems that the fact that
> "w" is a variable confuses mathematica?!

For your function,

   h[s_] = 1/(s^3 + 2s^2 + 2s + 1);

You can obtain the real and imaginary parts as follows:

   Simplify @ ComplexExpand @ Through @ {Re, Im} @ h[I w]

Cheers,
Paul

-- 
Paul Abbott                                   Phone: +61 8 9380 2734
School of Physics, M013                         Fax: +61 8 9380 1014
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Crawley WA 6009                      mailto:paul at physics.uwa.edu.au 
AUSTRALIA                            http://physics.uwa.edu.au/~paul


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