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Re: POLEZERO plots


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
CoefficientList[]

OLD: 

ncoeff = Table[
	Re[Coefficient[numerator,z^k]],{k,0,Length[zeros]}];

NEW:

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

OLD:

dcoeff = Table[
	Re[Coefficient[denominator,z^k]],{k,0,Length[poles]}];

NEW:

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.com
Wolfram Research, Inc.





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