Re: [python-control-discuss] call method

[Ryan K. <rk...@si...>]

poly1d makes it naturally vectorize so that the __call__ method could also
be used in Bode-type calculations:

In [16]: w = arange(1,5,0.5)

In [17]: control.freqresp(test,w)
Out[17]:
(array([[[ 0.31622777,  0.2981424 ,  0.2773501 ,  0.25607376,  0.23570226,
          0.21693046,  0.2       ,  0.18490007]]]),
 array([[[-0.32175055, -0.46364761, -0.5880026 , -0.69473828, -0.78539816,
         -0.86217005, -0.92729522, -0.98279372]]]),
 array([ 1. ,  1.5,  2. ,  2.5,  3. ,  3.5,  4. ,  4.5]))

In [18]: s_vect = 1.0j*w

In [18.5]: test(s_vect)
Out[18.5]:
array([ 0.30000000-0.1j       ,  0.26666667-0.13333333j,
        0.23076923-0.15384615j,  0.19672131-0.16393443j,
        0.16666667-0.16666667j,  0.14117647-0.16470588j,
        0.12000000-0.16j      ,  0.10256410-0.15384615j])


In [19]: freq_test = test(s_vect)

In [20]: abs(freq_test)
Out[20]:
array([ 0.31622777,  0.2981424 ,  0.2773501 ,  0.25607376,  0.23570226,
        0.21693046,  0.2       ,  0.18490007])

In [21]: angle(freq_test)
Out[21]:
array([-0.32175055, -0.46364761, -0.5880026 , -0.69473828, -0.78539816,
       -0.86217005, -0.92729522, -0.98279372])



--
Ryan Krauss, Ph.D.
Associate Professor
Mechanical Engineering
Southern Illinois University Edwardsville


On Thu, Jun 6, 2013 at 2:31 PM, Ryan Krauss <rk...@si...> wrote:

> FYI, I made this change in my local checkout code and ran a simple test
> and it is working:
>
> In [8]: test = control.TransferFunction(1,[1,3])
>
> In [9]: s1 = -1+2.0j
>
> In [10]: test(s1)
> Out[10]: (0.25-0.25j)
>
> In [11]: 1.0/(s1+3)
> Out[11]: (0.25-0.25j)
>
> Nothing too fancy, but solves my issue.
>
>
> --
> Ryan Krauss, Ph.D.
> Associate Professor
> Mechanical Engineering
> Southern Illinois University Edwardsville
>
>
> On Thu, Jun 6, 2013 at 1:47 PM, Ryan Krauss <rk...@si...> wrote:
>
>> I would like to submit some minor patches over the course of the summer
>> to help me completely get rid of my old controls module and switch over to
>> python-control for everything.  My most immediate need is for a __call__
>> method.  This method might not make any sense for a state-space system, but
>> for certain aspects of my modeling work, I need to evaluate transfer
>> functions at certain numerical values of s.
>>
>> I would propose something like this:
>>
>> def __call__(self, s):
>>     """Evaluate a transfer function at s."""
>>     N_poly = poly1d(squeeze(self.num))
>>     D_poly = poly1d(squeeze(self.den))
>>     return N_poly(s)/D_poly(s)
>>
>>
>> It could also include a check that self is SISO and possibly throw an
>> exception if it is not (pretty sure that poly1d will throw one if we pass
>> in a vector of coefficients that isn't 1d).
>>
>> Would this be welcome?  Is there anything I should tweak?
>>
>> Thanks,
>>
>> Ryan
>>
>> --
>> Ryan Krauss, Ph.D.
>> Associate Professor
>> Mechanical Engineering
>> Southern Illinois University Edwardsville
>>
>
>