# [SciPy-user] (newbie) IIR, is there a MatLab "filter" equivalent ?

Stef Mientki s.mientki at ru.nl
Fri Dec 22 17:58:26 CST 2006

```hello,

this might be a dumb question,
if so, sorry for my ignorance,
but my math is rusted,
and I'm a completly newbie (to Python),
I haven't even installed Python on my computer yet ;-)

I'm evaluating some packages for easy data-acquisition and (real-time)
data-analysis,
specific for bio-physical signals (e.g. ECG, EOG, etc).

I've seen LabView and threw it in the recycle bin.
I've seen MatLab and decided it needed a user friendly wrapper,
after which it looks quit powerfull.

After my positive experiences with MatLab scripting (didn't realize
scripting could be so fast),
I searched for more and found 2 other interesting packages (both open
source),
- SciLab : almost identical to MatLab, and with an equivalent Simulation
module
- Python + huge collection of tools : suited for a wide range of
platforms, even for small PIC micro controllers

I quickly read some documents about NumPy and SciPy,
and most functions I need are there, even the clip function which is
missing in MatLab.
But I couldn't find the equivalent of the MatLab "filter" function: y =
filter(b,a,X)
The filter function is implemented as a direct form II transposed
structure,
y(n) = b(1)*x(n) + b(2)*x(n-1) + ... + b(nb+1)*x(n-nb)
- a(2)*y(n-1) - ... - a(na+1)*y(n-na)

Is there a Python equivalent to this filter function ?

I tried to look in the archives of this mailinglist, but that's not a
job for humans.
(btw, does anyone has the complete list archive in Thunderbird format ?)

What I also couldn't find
( I do admit that Python information is overwhelming, but maybe that's
the problem for newbies)
is there a toolbox to generate the filter polynomes ?

thanks,
Stef Mientki
```

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