# How to solve the double summation of the given expression

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vivek raja on 24 Aug 2017
Commented: Yago Moreno on 5 Sep 2019
I am unable to find out how can we find the double summation of the expression which has a lot of variables in it
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Jan on 24 Aug 2017
What have you tried so far? I would not call this "a lot of" variables, but as long as you do not explain their meaning, posting code is based on guessing only. Please provide any details.

njj1 on 24 Aug 2017
Edited: njj1 on 24 Aug 2017
A blunt force method would be to have two for loops, one nested in the other. In the inner for loop, sum over the 'i' variables, and in the outer loop sum over the 'p' variables. This could look like:
AF = [];
for p=1:length(P)
for i=1:Np
AF = AF + I(p,i)*exp(1i*k*r(p)*sin(theta)*cos(phi0 - phi(p,i)) + alpha(p,i))
end
end
AF = 1 + AF;
A more elegant solution would use matrix operations.
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Yago Moreno on 5 Sep 2019
Hi njj1,
I was wondering how you would use matrix operations for double sums. Could you give more details or re-direct me to another post? I have not found posts explaining this method.
Thanks!