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?!

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
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```

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