[SciPy-Dev] Strange code in scipy.signal.decimate

[Warren Weckesser]

On 10/18/18, Daniele Nicolodi <daniele at grinta.net> wrote:
> On 18-10-2018 15:28, Paul Hobson wrote:
>> Dan,
>>
>> I might be missing something, but dlti returns a subclass of
>> LinearTimeInvariant. Point is, it's not a tuple, but a class with
>> multiple attributes and method. Simple tuple unpacking won't likely work
>> unless the authors of LinearTimeInvariant really went out of their way
>> to make it so.
>
> The point is not to go through the `dlti` class at all.
>
> Please look at the replacement code I posted: it works.
>


There have been several incremental changes to that function over the
years.  I suspect the last person to change it simply did not notice
that the code could be simplified.  Your proposed change looks good.

Warren


> Cheers,
> Dan
>
>> -Paul
>>
>> On Thu, Oct 18, 2018 at 1:58 PM Daniele Nicolodi <daniele at grinta.net
>> <mailto:daniele at grinta.net>> wrote:
>>
>>     Hello,
>>
>>     I was having a look at the scipy.signal.decimate() function and I
>>     noticed some strange looking code:
>>
>>         elif ftype == 'iir':
>>             if n is None:
>>                 n = 8
>>             system = dlti(*cheby1(n, 0.05, 0.8 / q))
>>             b, a = system.num, system.den
>>
>>     This is used to setup the anti aliasing low pass filter. What I don't
>>     understand is the dance to obtain the IIR numerator and denominator
>>     coefficients. Couldn't the above be simply as the code below?
>>
>>         elif ftype == 'iir':
>>             if n is None:
>>                 n = 8
>>             b, a = cheby1(n, 0.05, 0.8 / q)
>>
>>     Am I missing something?
>>
>>     Thanks!
>>
>>     Cheers,
>>     Dan
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