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Convolution of two equally sized arrays [message #41964]

Thu, 09 December 2004 15:03

Benjamin Hornberger is currently offline

Benjamin Hornberger
Messages: 258
Registered: March 2004

Senior Member

Hi all,

IDL's convol() function requires the kernel to be smaller than the
array. Any ideas why?

According to Brigham, "The Fast Fourier Transform", the discrete
convolution is defined as

y(k) = Sum(i=0,N-1) x(i) * h(k-i)

where both x(k) and h(k) are periodic functions with period N.

So I would think that if I have two equally gridded functions (two
arrays a and b of equal size), I can convolve them by

result = convol(a, b, /edge_wrap, center=0)

and interchanging a and b should give the same result. I hope I
understood the center keyword right.

But anyway, it doesn't work because IDL wants the kernel to be smaller
than the array. Do I have to write my own convolution function?

Any hints?

Thanks,
Benjamin

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