[Octave-bug-tracker] [bug #49996] signal package: cheby2 produces zeros that are not quite complex conjugate pairs

[Bill Lash]

Follow-up Comment #7, bug #49996 (project octave):

In the butterworth example mentioned below, it is the poles that are not
complex conjugate pairs.  This could also be an issue in the cheby2 case and
we just don't have a test case that finds it. It is a little more tricky in
the pole case, since the number of poles can be odd

I'll try taking a look at butter to see if there is something that can be done
there.

I think that in all cases, the prototype filter that is generated will have
complex conjugate poles and zeros with the differences small enough to pair,
but then when the frequency is warped to generate a filter with a different
cutoff or change from low-pass to high-pass, band-pass or band-stop, the small
difference is amplified.


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