[Scipy-tickets] [SciPy] #581: chebwin improvement: use the Chebyshev polynomial

SciPy scipy-tickets@scipy....
Fri Jan 11 09:48:36 CST 2008


#581: chebwin improvement: use the Chebyshev polynomial
--------------------------+-------------------------------------------------
 Reporter:  akumar        |       Owner:  somebody
     Type:  defect        |      Status:  new     
 Priority:  high          |   Milestone:  0.7     
Component:  scipy.signal  |     Version:          
 Severity:  normal        |    Keywords:          
--------------------------+-------------------------------------------------
 Hi!

 I noticed that the Dolph Chebyshev I wrote earlier was not working due to
 some issues with the hyperbolic functions. For example:

 {{{
 In [2]: signal.chebwin(20, 50)
 Out[2]:
 array([ NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,
         NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN])

 In [3]: signal.chebwin(10, 50)
 Out[3]: array([ NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,  NaN,
 NaN])
 }}}

 I prodded it a bit, and found that the issue lies with the way I am
 calculating the Chebyshev polynomial. After two hours, I gave up and tried
 using the special.chebyt function, only to find that it works perfectly.

 All values are matching the Matlab generated ones (from my test). I am
 attaching diff of signaltools.py, which applies against the HEAD of SVN.
 Please consider adding it.

 Thanks.

 Kumar Appaiah

-- 
Ticket URL: <http://scipy.org/scipy/scipy/ticket/581>
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