[SciPy-User] faster interpolations (interp1d)

James McCormac jmccormac01@qub.ac...
Tue Mar 1 05:01:07 CST 2011


Hi eat,
Yes this code works fine, its not actually that bad on a 2x500 arrays  
~5 but the 500 length arrays are the shortest I can run with. I am  
analyzing CCD images which can go up 2000x2000 in length and breadth,  
meaning 2x2000 1d arrays after collapsing the spectra. This takes >20  
sec per image which is much too long. Ideally the id like it to run as  
fast as possible (depending on how much accuracy I can maintain).

Yes the code works fine its just a little slow, I've put timers in and  
98% of the time is taken up by the interpolation.  Any improvement in  
performance would be great. I've slimmed  down the rest of the body as  
much as possible already.

Cheers
James


On 1 Mar 2011, at 07:31, eat wrote:

> Hi James,
>
> On Mon, Feb 28, 2011 at 5:25 PM, James McCormac  
> <jmccormac01@qub.ac.uk> wrote:
> Hi eat,
> you sent me a suggestion for faster 1d interpolations using matrices  
> a few
> weeks back but I cannot find the email anywhere when I looked for it
> today.
>
> Here is a better explanation of what I am trying to do. For example  
> I have
> a 1d array of 500 elements. I want to interpolate them quadratically  
> so
> each array becomes 10 values, 50,000 in total.
>
> I have 500x500 pixels and I want to get 0.01 pixel resolution.
>
> code snipet:
> # collapse an image in the x direction
> ref_xproj=np.sum(refarray,axis=0)
>
> # make an array for the 1d spectra
> x = np.linspace(0, (x_2-x_1), (x_2-x_1))
>
> # interpolation
> f2_xr = interp1d(x, ref_xproj, kind='quadratic')
>
> # new x array for interpolated data
> xnew = np.linspace(0, (x_2-x_1), (x_2-x_1)*100)
>
> # FFT of interpolated spectra
> F_ref_xproj = fftpack.fft(f2_xr(xnew))
>
> Can I do this type of interpolation faster using the method you  
> described
> before?
> I'll misinterpreted your original question and the method I  
> suggested there is not applicable.
>
> To better understand your situation, few questions:
> - what you described above; it does work for you in technical sense?
> - if so, then the problem is with the execution performance?
> - what are your current timings?
> - how much you'll need to enhance them?
>
> Regards,
> eat
>
> Cheers
> James
>
>
>
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-------------------------------------------------
James McCormac					
jmccormac01@qub.ac.uk
Astrophysics Research Centre
School of Mathematics & Physics
Queens University Belfast
University Road,
Belfast, U.K
BT7 1NN,
TEL: 028 90973509






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