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