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Topic: Need help in doing fft for a large matrix
Replies: 3   Last Post: Feb 8, 2013 8:50 AM

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Derek Goring

Posts: 3,892
Registered: 12/7/04
Re: Need help in doing fft for a large matrix
Posted: Feb 7, 2013 5:43 PM
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On Friday, February 8, 2013 9:05:58 AM UTC+13, anyone wrote:
> On Thu, 07 Feb 2013 11:06:42 -0800, TideMan wrote:
>
>
>

> > On Friday, February 8, 2013 2:34:08 AM UTC+13, Gupta wrote:
>
> >> Hello...i ma trying to do abs(fft(y))) where y a large matriy of size
>
> >> 1x8388608. when i am running the code, at this line the program was
>
> >> getting terminated without running remaining commands. was the problem
>
> >> is with size of the matrix or memory of matlab or fft funtion. when i
>
> >> do this operation for a mtrix of size 1x4194304 it was working perfect.
>
> >
>
> > Why are you even trying to take the FFT of such a long series?
>
>
>
> My bet: that's what (s)he wants to do.
>
>
>

> > The resulting spectrum will be so noisy, you won't be able to interpret
>
> > it.
>
>
>
> Not necessarily, depends on signal content.
>
>
>

> > Split the signal into 10 or more blocks, take the FFT of each, then
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> > average the results and take the abs of the first half. This will give
>
> > a nice smooth spectrum.
>
>
>
> ...and you necessarily lose detail on components that are relatively uncorrelated to a target signal. "A nice smooth
>
> spectrum" was not stated as any kind of requirement. My speculation: the OP has a hardware problem.


And my speculation: OP doesn't know what (s)he is doing and needs to think about what (s)he will get out of the transformation before buying new RAM.



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