Sushanth,
The method for doing this depends on your function f(x,N).
If this function works with vectors, then the easiest function for this would be something in the form:
N = 1:100;
sum_function = @(x) sum(f(x, N)); % Assuming f(x,N) can take a vector N and is already defined
Then, calling sum_function(10) would provide the summation with x = 10.
Alternatively, you could make a function that only accepts X, and a range to sum over, and go through a for loop summing the values over that range. However, that is up to you.
Hope that helps,
Michael
