[Octave-bug-tracker] [bug #63393] [octave forge] (control) Bode plot problem. Different results between MATLAB and Octave.

[Torsten Lilge]

Follow-up Comment #22, bug #63393 (project octave):

It seems that the bode plot of proportional but unstable systems starts with a
phase not equal to zero in Matlab, like, e.g.


G = tf (1,[1 -2 1]);
bode (G)


Therefore, the phase for your example in Octave looks correct, except for the
phase at 400 < w < 1000 when not using a sufficiently high number of frequency
samples.

Actually, when applying Dimitri's patch in comment #17 and the frequency range
from comment #13, the bode plot looks good on my system.

To summarize, we have the following two issues:
* Evaluation of polynomials not numerically robust
* Numerical issues (especially in the phase) depend on the number frequency
samples of the bode plot
Or am I missing something?



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