[Numpy-discussion] Another reality check

Jochen Schröder cycomanic@gmail....
Mon Jul 12 03:14:15 CDT 2010


On 07/12/2010 12:36 PM, David Goldsmith wrote:
> On Sun, Jul 11, 2010 at 6:18 PM, David Goldsmith
> <d.l.goldsmith@gmail.com <mailto:d.l.goldsmith@gmail.com>> wrote:
>
>     In numpy.fft we find the following:
>
>     "Then A[1:n/2] contains the positive-frequency terms, and A[n/2+1:]
>     contains the negative-frequency terms, in order of decreasingly
>     negative frequency."
>
>     Just want to confirm that "decreasingly negative frequency" means
>     ..., A[n-2] = A_(-2), A[n-1] = A_(-1), as implied by our definition
>     (attached).
>
>     DG
>
>
> And while I have your attention :-)
>
> "For an odd number of input points, A[(n-1)/2] contains the largest
> positive frequency, while A[(n+1)/2] contains the largest [in absolute
> value] negative frequency."  Are these not also termed Nyquist
> frequencies?  If not, would it be incorrect to characterize them as "the
> largest realizable frequencies" (in the sense that the data contain no
> information about any higher frequencies)?
>
> DG
>
I would find the term the "largest realizable frequency" quite 
confusing. Realizing is a too ambiguous term IMO. It's the largest 
possible frequency contained in the array, so Nyquist frequency would be 
correct IMO.

>
>
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