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[Octave-bug-tracker] [bug #49996] [octave forge] (signal) cheby2 produce

From: Mike Miller
Subject: [Octave-bug-tracker] [bug #49996] [octave forge] (signal) cheby2 produces zeros that are not quite complex conjugate pairs
Date: Tue, 3 Apr 2018 18:17:41 -0400 (EDT)
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:59.0) Gecko/20100101 Firefox/59.0

Follow-up Comment #15, bug #49996 (project octave):

Since cplxpair has been fixed in Octave, the 'butter' example mentioned in
comment #4 is no longer a problem.

To sum up, the problem appears limited to the vector of zeros returned by

In (not-yet-released) Octave 4.4, the cplxpair function forces the results
that are near-conjugates, within the given (or default) tolerance, to be

So if Octave 4.4 is active, we could use cplxpair within the cheby2 function
to force the zeros to be exact conjugates, with some suitable tolerance.

Or some other change to ensure that the complex zeros are conjugate pairs.

Is there any reason to make a change in sftrans.m as suggested in comment #14?
That is a much broader change to address a narrow problem in cheby2.


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