[Octave-patch-tracker] [patch #10352] adding islinphase.m

[Leonardo]

Follow-up Comment #5, patch #10352 (project octave):

Once again,

For the filter defined by b = [1 -1]; a = [1 -2]; the angle will be:

arg((1 - e^(-j ω))/(1 - 2 e^(-j ω)))

and the group delay will be:

d/dω(arg((1 - e^(-j ω))/(1 - 2 e^(-j ω)))) = (π j e^(j ω) δ((-1 + e^(j
ω))/(-2 + e^(j ω))))/(e^(j ω) - 2)^2

and we may conclude that there is a discontinuity at ω = 0

reference:
https://www.wolframalpha.com/input?i=angle+%28+%281+-+e%5E%28-j%CF%89%29%29+%2F+%281+-+2e%5E%28-j%CF%89%29%29+%29


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