[Octave-bug-tracker] [bug #56851] butter returns incorrect value

[Henk Borsje]

Follow-up Comment #3, bug #56851 (project octave):

It sure does look like a round-off error, but one with grave consequences. 
This filter spec is not unreasonable.  Changing the spec to e.g.
butter(4,1/28800) works correctly, as well as butter (5,1/28801).  The
resulting sum(a) = 0 causes a division by 0 when one tries to use the filter. 
 MATLAB handles this case correctly, so it sounds like a bug to me.

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