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MathGroup Archive 1999

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Re: POLEZERO plots

  • To: mathgroup at
  • Subject: [mg19069] Re: POLEZERO plots
  • From: "P.J. Hinton" <paulh at>
  • Date: Thu, 5 Aug 1999 01:34:55 -0400
  • Organization: "Wolfram Research, Inc."
  • References: <7o5ilf$>
  • Sender: owner-wri-mathgroup at

On 2 Aug 1999, John Cogill wrote:

> The excellently written notebook, from Mathsource, seems to have
> errors in both the numerator and the denominator of the
> digitized transfer function.

It is not clear from your introduction exactly _which_ notebook you are
talking about?  Do you have a title or a MathSource item number for the
notebook?  I am assuming that you're speaking of MathSource Item 0205-546
"Filter Design by Pole-Zero Placement" by H. Joel Trussell.

> My Mathematica 4 complains "ivar .. " until I change the zeros to ones
> in both cases.
> I feel I must be missing something.

The problem is with the author's use of the Coefficient[] function, with
which the "ivar" tag is associated.  Mathematica does not allow you to
invoke Coefficient[] with an integer (1). 

If you rewrite the assignments for ncoeff and dcoeff so that they use


ncoeff = Table[


ncoeff = Map[Re, CoefficientList[numerator,z]];


dcoeff = Table[


dcoeff = Map[Re, CoefficientList[denominator,z]];

The code works fine.

I am copying the notebook's author in on this message so that he can fix
the notebook and resubmit an update to MathSource if he wishes.

P.J. Hinton
Mathematica Programming Group           paulh at
Wolfram Research, Inc.

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