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dfourt [message #90829]

Tue, 21 April 2015 16:35

beppe89
Messages: 1
Registered: April 2015

Junior Member

Hi everyone,

I am a beginner in the use of IDL and and I need some help. I need to write a program that calculates the inverse of the discrete fourier transform calculated by the dfourt.pro.
I know that dft.pro calculates the inverse, but I really need the one from dfourt.pro.

Thanks,
--
beppe89
http://compgroups.net/comp.lang.idl-pvwave/

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Re: dfourt [message #90833 is a reply to message #90829]

Fri, 24 April 2015 11:44

Matthew Argall
Messages: 286
Registered: October 2011

Senior Member

Looking at the code
http://www.arm.ac.uk/~csj/idl/CLEAN/dfourt.pro

It seems pretty easy to do. They appear to be building the Fourier transform as described in any undergraduate mathematical methods text (e.g. Boas). Essentially, the inverse transform would be

ifft = complex(0, 0)
for i = 0, npts - 1
ifft = ifft + complex( A[i] * cos(f[i]*t), B[i] * sin(f[i]*t)
endfor

Where A and B are the real and complex fourier coefficients, t is time, and f is frequency.

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