[Numpy-discussion] Optimizing recursive loop - updated example

[Robert Elsner]

Yes I did. Slicing and Cython do not mix too well. Using an explicit
loop fixes the problem. In case anybody is interested the code is attached.

Thanks for your help
Robert

On 25.07.2011 12:30, Robert Elsner wrote:
> Thanks for the hint. I thought about Cython myself but I was unable to
> get even the slightest speed gain out of it.
> Here is the equivalent Cython code with the timing and setup.py. I typed
> (I think). Am I missing something obvious?
>
> Cheers
> Robert
>
> On 25.07.2011 01:38, Joon Ro wrote:
>> For those cases where you cannot vectorize the operation, numpy is
>> usually does not help much.
>> Try using Cython. You will be able to compile the part of the code and
>> the loop will be much faster (can be more than 100 times faster).
>>
>> http://docs.cython.org/
>>
>> -Joon
>>
>>
>> On Sun, 24 Jul 2011 18:10:14 -0500, Robert Elsner
>> <mlist at re-factory.de> wrote:
>>
>>> Boiled it down a bit more to only include code that actually takes time.
>>> First time around I found the other variant more instructive because it
>>> shows the discrepancy between the DCT and the loop but might be
>>> confusing. Thus here the bare minimum that correctly calculates the
>>> coefficients of the first derivative from the coefficients of the
>>> Chebyshev polynomials.
>>>
>>> Cheers
>>> Robert
>>>
>>> On 25.07.2011 00:43, Robert Elsner wrote:
>>>> Hey Everybody,
>>>>
>>>> I am approximating the derivative of nonperiodic functions on [-1,1]
>>>> using Chebyshev polynomials. The implementation is straightforward and
>>>> works well but is painfully slow. The routine wastes most of its
>>>> time on
>>>> a trivial operation (see comment in the code)
>>>> Unfortunately the spectral coefficients are calculated recursively and
>>>> thus I haven't found a way to speed up the code. I am aware of list
>>>> comprehensions, the speed advantage of calling native numpy functions
>>>> etc. But no luck yet finding an alternate formulation that speeds up
>>>> the
>>>> calculation. I attached a stripped down variant of the code. I am very
>>>> grateful for tips or directions where to look for a solution (well I
>>>> know writing a small C extension might be the way to go but Id love to
>>>> have speedy Python)
>>>>
>>>> Note: The DCT takes almost no time compared to the statement in the
>>>> loop.
>>>>
>>>> Cheers
>>>> Robert
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> NumPy-Discussion mailing list
>>>> NumPy-Discussion at scipy.org
>>>> http://mail.scipy.org/mailman/listinfo/numpy-discussion
>>
>
>
> _______________________________________________
> NumPy-Discussion mailing list
> NumPy-Discussion at scipy.org
> http://mail.scipy.org/mailman/listinfo/numpy-discussion

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/numpy-discussion/attachments/20110725/5447b149/attachment.html>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: optimization.pyx
URL: <http://mail.python.org/pipermail/numpy-discussion/attachments/20110725/5447b149/attachment.ksh>