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

[Mike Miller]

Follow-up Comment #13, bug #49996 (project octave):

Yes, the 1e-3 approximation I posted in comment #10 has the same problem in
Octave as the original


>> [z, p, k] = cheby2 (6, 40, [.001, .983]);
>> cplxpair (z)
error: cplxpair: could not pair all complex numbers
error: called from
    cplxpair at line 118 column 9


But the values that SciPy computes for the same filter design call behave when
pasted into Octave:


>> z2 = [(-0.99866962186808894-0.051565360057387599j),
 (-0.99928680643819134-0.037760806116408051j),
 (-0.99990441719062173-0.013825935146777633j),
 (-0.99990441719062173+0.013825935146777633j),
 (-0.99928680643819134+0.037760806116408051j),
 (-0.99866962186808894+0.051565360057387599j),
 (0.99999539574401186+0.0030345495179681286j),
 (0.99999753249436207+0.0022214871566177065j),
 (0.99999966940456275+0.0008131363754524236j),
 (0.99999966940456275-0.0008131363754524236j),
 (0.99999753249436207-0.0022214871566177065j),
 (0.99999539574401186-0.0030345495179681286j)];
>> cplxpair (z2)
ans =

  -0.999904417190622 - 0.013825935146778i
  -0.999904417190622 + 0.013825935146778i
  -0.999286806438191 - 0.037760806116408i
  -0.999286806438191 + 0.037760806116408i
  -0.998669621868089 - 0.051565360057388i
  -0.998669621868089 + 0.051565360057388i
   0.999995395744012 - 0.003034549517968i
   0.999995395744012 + 0.003034549517968i
   0.999997532494362 - 0.002221487156618i
   0.999997532494362 + 0.002221487156618i
   0.999999669404563 - 0.000813136375452i
   0.999999669404563 + 0.000813136375452i




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