Hello all Would someone please tell me how negative and positive frequencies are stored in the output of the Numerical Python fft? Cheers, Daniel
print FFT.fft.__doc__ fft(a, n=None, axis=-1)
Will return the n point discrete Fourier transform of a. n defaults to the length of a. If n is larger than a, then a will be zero-padded to make up the difference. If n is smaller than a, the first n items in a will be used. The packing of the result is "standard": If A = fft(a, n), then A[0] contains the zero-frequency term, A[1:n/2+1] contains the positive-frequency terms, and A[n/2+1:] contains the negative-frequency terms, in order of decreasingly negative frequency. So for an 8-point transform, the frequencies of the result are [ 0, 1, 2, 3, 4, -3, -2, -1]. This is most efficient for n a power of two. This also stores a cache of working memory for different sizes of fft's, so you could theoretically run into memory problems if you call this too many times with too many different n's.
Hmph. The style guide says I should've put a blank line on the end of that docstring. But I don't think there was a style guide then. w On Tue, 26 Jul 2005, Daniel Sheltraw wrote:
Hello all
Would someone please tell me how negative and positive frequencies are stored in the output of the Numerical Python fft?
Cheers, Daniel
------------------------------------------------------- SF.Net email is sponsored by: Discover Easy Linux Migration Strategies from IBM. Find simple to follow Roadmaps, straightforward articles, informative Webcasts and more! Get everything you need to get up to speed, fast. http://ads.osdn.com/?ad_id=7477&alloc_id=16492&op=click _______________________________________________ Numpy-discussion mailing list Numpy-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/numpy-discussion
participants (2)
-
Daniel Sheltraw
-
Warren Focke