Fourier series for a random function

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sukharef
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Hello!

My problem consists of :
there is a representation of an uneven surface in terms of Fourier series with random coefficients:
Equation: zeta(x, y) equals the double sum over m and n of P(m, n) times exp(i 2 pi m x / L + i 2 pi n y / L).


The random coefficients are under several conditions:
Two-part equation block with a Russian-language note: the average of P(m, n) is 0, and <P(m, n) P*(m', n')> equals 0 when m is not m' and n is not n', and (2π/L)² · ¼ · W(2πm/L, 2πn/L) when m = m' and n = n'.


W - function is undefined.

Maybe you've confronted with such kind of expressions.
The question is : how to determine P-coefficients? Maybe they can be presented by means of some well-known probability density distributions or smth with a help of Monte-Carlo numerical methods?

Thank you in advenced.
 
All the conditions say the coefficients have mean 0 and are uncorrelated. Otherwise any distributions with the given second moments is possible.

There appears to be an error in the Russian (I can't read Russian). The correlation =0 for m≠m' OR n≠n' while the correlation is the second moment for m=m' AND n=n'.