[Octave-bug-tracker] [bug #41958] signal package: fir2 interpolation incompatible with octave 3.8

[Mike Miller]

Update of bug #41958 (project octave):

                 Release:                   other => 3.8.0                  
                 Summary: signal package: fir2 function incorrect results for
high-pass, band-pass, band-stop filters => signal package: fir2 interpolation
incompatible with octave 3.8

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Follow-up Comment #2:

Moreover, I can confirm that this bug affects the signal package under Octave
3.8 but not under 3.6 or earlier. The reason is a change in the interp1
function to no longer allow piecewise linear interpolation of discontinuous
functions. A change to fir2 is needed to do essentially what it used to do
with interp1 without relying on this now-unsupported feature.

Specifically, something like this


x = interp1 ([0 0.5 0.5 1], [0 0 1 1], linspace (0, 1, 1000));


used to give x that was equivalent to


x = [zeros(1,500) ones(1,500)];


and now no longer does in Octave 3.8.

I am assigning myself to this bug, but please feel free to provide a patch if
this is of interest to anyone else.

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