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MathGroup Archive 2012

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InverseZTransform numerical issue on some expression, version 8.0.4

  • To: mathgroup at smc.vnet.net
  • Subject: [mg126784] InverseZTransform numerical issue on some expression, version 8.0.4
  • From: "Nasser M. Abbasi" <nma at 12000.org>
  • Date: Thu, 7 Jun 2012 05:20:02 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • Reply-to: nma at 12000.org

Using 8.0.4 on windows 7

---------------------------
InverseZTransform[1/(0.9512294245007143 -1.9512294245007142  z+z^2),z,n]
---------------------------

does NOT generate an answer.  But

------------------------------
InverseZTransform[1/(0.9512294245 -1.9512294245 z+z^2),z,n]
------------------------------

does. I simply chopped few digits (kept removing one digit
at a time until it worked)

    0.9512294245007143->0.9512294245
and
   1.9512294245007142->1.9512294245

In order to get a result since I had a feeling it is a numerical
issue.

screen shot

http://12000.org/tmp/060612/invz.png

question is: Is this due to numerical issue? and
how to better handle this whole thing. Clearly what I did
above is not what I would do all the time. May be I am
missing an option or something else. Because in a larger
program, I would need to make sure InverseZTransform
worked all the time or a way to check if it did not work.

thanks
--Nasser



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