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Re: How to define the coefficients of a polynomial to be real?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg100932] Re: How to define the coefficients of a polynomial to be real?
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 18 Jun 2009 06:18:16 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <h1cvbi$ji2$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

$Assumptions = {Element[a0, Reals]}

and

Simplify[Re[a0]]

will work.

Regards
   Jens

BHUPALA wrote:
> I have a 10th order polynomial (a0+a1 z+a2 z^2 + ... + an z^10). I
> want to define all the coefficients to be real. I want to substitute z
> = 1+i and extract only real part of it.
> 
> I have done this by defining
> 
> Element[a0,Reals];
> Element[a1,Reals];
> .
> .
> .
> Element[a10,Reals];
> 
> Ply = a0+a1z+a2 z^2 + ... + an z^10;
> Ply/. z-> 1+I
> 
> I am getting
> 
> -2 Im[a2]+Re[a0+(1+i) a1-(2-2i)a3- 4a4]
> 
> which I should not have got as I have defined already defined the
> coeffs to be real.
> 
> Any help please!
> 
> bhupala
> 


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