[SciPy-Dev] Proposal: calling signal.lti object returns transfer function value

Juan Luis Cano juanlu001@gmail....
Tue Jul 23 05:29:38 CDT 2013


On 07/20/2013 05:39 PM, Ralf Gommers wrote:
>
>
>
> On Tue, Jul 16, 2013 at 4:49 PM, Juan Luis Cano <juanlu001@gmail.com 
> <mailto:juanlu001@gmail.com>> wrote:
>
>     Hello all,
>
>     I've been trying the scipy.signal module lately for some easy
>     things and
>     I had an idea, but I thought it would be better to bring it up in the
>     mailing list before filing a PR on GitHub.
>
>     My proposal is to implement the __call__ method on signal.lti
>     objects so
>     it returns the value on the transfer function.
>
>     I took the idea from the `bode` function. This line:
>
>          y = numpy.polyval(sys.num, jw) / numpy.polyval(sys.den, jw)
>
>     (https://github.com/scipy/scipy/blob/v0.12.0/scipy/signal/ltisys.py#L940)
>
>     could be moved to signal.lti.__call__, and then in `bode` write
>
>          y = sys(jw)
>
>     The detail is trivial (so is the implementation) but I think it
>     would be
>     a useful thing. What do others think? Shall I open a pull request?
>
>
> Not sure, is writing
>     y = lti_sys(jw)
> instead of
>     jw, y = lti_sys.freqresp(jw)
> clearer and umambiguous? It may make sense, but would be good to get 
> the opinion of some users on this.
>
> Ralf

I am sorry but I was unaware of the freqresp function, probably it's the 
clearest way. Maybe it should be used in the `bode` function too.

Juan Luis Cano
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