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Solving a 2D Fourier Transform

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HI Folks,
I don't do much in the Fourier arena so please forgive the naivete of this question. emoticon
I am trying to solve the following 2D Fourier transform (z is a constant):
FourierTransform[1/Sqrt[x^2 + y^2 + z^2], {x, y}, {u, t}]
After some time, Mathematica simply returns the original formula. Similar scenario, if I try to solve the corresponding integral directly:
Integrate[Exp[2 Pi I (m*x + n*y)]/Sqrt[x^2 + y^2 + z^2], {x, 0, 1}, {y, 0, 1}]
Any advice?

Cheers,
Nick
POSTED BY: Nick Pizzi
Answer
7 months ago
It may not be an integral that is doable in closed form.  If you first do the x-Integral, the remaining y-integral is (assuming that z is Real)
FourierTransform[
Sqrt[2/Pi] BesselK[0, u Sqrt[y^2 + z^2] Sign[u]], {y}, {t},
Assumptions -> {z \[Element] Reals}]
 Which returns unevaluated. 
POSTED BY: David Reiss
Answer
7 months ago
Hi David,
Thanks very much for your comment. Yes, z is Real and positive. I will focus on a numerical solution. I had thought that perhaps I was missing something obvious with respect to a closed form solution.

Cheers.
POSTED BY: Nick Pizzi
Answer
7 months ago
Also note, FourierTransform transform is defined over {- Infinity, + Infinity}, while your 2nd integrals have range {0,1}.
POSTED BY: Sam Carrettie
Answer
7 months ago
Thanks Sam.
POSTED BY: Nick Pizzi
Answer
7 months ago