for your info: ch. 11 mbe: fast fourier transforms

Robert Dodier wrote:
> On 5/5/09, dlakelan <dlakelan at street-artists.org> wrote:
>
>   
>> Robert Dodier wrote:
>>     
>>> Well, I dunno. The computed results match the stated definition --
>>> I've verified that directly. We could pick a different definition, I
>>> guess, if it could make the results more useful or comprehensible.
>>>       
>> Yes perhaps this is the thing to do. I think the point is to help the
>> users of the fft routine when doing something relatively standard, such
>> as fft transforming a real function, and trying to manipulate the
>> individual frequencies.
>>     
>
> Having thought it over, I'm opposed to changing the definition of
> the FFT for Maxima.
>
> I'm pretty sure the FFT definition should be general, and not
> embody some particular assumption about what people are trying
> to do. Maybe in some cases it's safe to make assumptions, but it
> certainly isn't for FFT.
>   
I agree with this. The FFT is pretty-well standardized to be what Maxima
is doing today. If you change it to fit your needs, it will certainly
collide with my needs which are usually exactly the form that Maxima
returns today.

However, I vaguely recall that matlab has an fftshift (fftsplit?)
function that takes the right half and puts in before the left half so
that the zero frequency term is in the middle. I only used this for
plotting so that you get the expected amplitude spectrum plot (for
low-pass signals).

Ray