[Octave-bug-tracker] [bug #60423] [octave forge] (signal) buttord incorrect result

[Charles Praplan]

Follow-up Comment #4, bug #60423 (project octave):

buttord calculates the minimum filter order to satisfy a specification.
In most cases, the theoretical minimum order is not an entire number and
must be rounded up.

This theoretical order would let the response touch both the pass band
corner and the stop band corner.
The filter with the rounded order will not touch both corners.

You have the choice to let the response touch the pass band corner, the
stop band corner or neither one, by choosing Wn (value passed to butter)
respectively as WC_P, WC_S or any value between WC_P and WC_S.

More generally, note that Matlab and Octave may deliver different results
which are both correct.
Some problems have several possible solutions, as the above example shows.
Another example is the way to pair zeros and poles in second order sections...

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