It sounds like you are trying to perform numerical double integration. Have you tried using the function “integral2”?
Here’s how you might do that for your example:
>>fun = @(x,y) exp(x.*y); //handle to function to be integrated
>>llim = -N/2*a; //define limits of integration
>>ulim = (N/2-1)*a;
>>q = integral2(fun,llim,ulim,llim,ulim);
Please refer to the following documentation for more information about the “integral2” function: http://www.mathworks.com/help/matlab/ref/integral2.html
