[SciPy-user] Problems with filter design

Kumar Appaiah akumar at iitm.ac.in
Sat Jan 20 23:44:48 CST 2007

On Sat, Jan 20, 2007 at 11:09:43PM -0600, Robert Kern wrote:
> It's a subtle bug. Wn is being coerced to an array in
> iirfilter(). When Wn is a scalar, it becomes a rank-0
> array. Unfortunately, there was a bit of inaccurate type-checking in
> lp2lp and lp2hp that assumed that if the type of wo was an array,
> then it would be a (2,)-array of 2 critical frequencies, not a
> ()-array (and don't ask me whether or not having two critical
> frequencies makes sense.  It's been a long time since I took my
> signal processing class).

It's quite all right. Signal processing isn't something one is too
good at unless one is in it throughout!

> I've checked in a workaround.

Which leads me to think; haven't people been using these functions?
They seem to have quite a few unpolished stuff.

Another example is the docstring for signal.ellipord. If you notice,
at the bottom, it says "Chebyshev" instead of "Elliptic"; obviously,
it has been overlooked while doing a copy paste!

Anyway, when I find a fault like this, I still feel I should post it
on the list to ensure others are facing the same problems, rather than
call for a bug filing straightaway. Is this OK?

Thanks for the quick response!

Kumar Appaiah,
462, Jamuna Hostel,
Indian Institute of Technology Madras,
Chennai - 600 036

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