How to sum a specified range of rows in a matrix?

Hi I'm tryign to sum up sections of a 5000x6482 matrix. I'd like to sum the 1st row with the 17th row, 33rd row and so so on in step sizes of 16 up to 5000. And 2nd row with the 18th row, 34th row etc.

I have tried the code below;

    for j = 1:5000
        for n = 1:16:6482
            test(j,n) = sum(raw_signal(j,n));
        end
    end

This gives me a 4993x6482 matrix with values in the first row, 17th row, 33rd row... in stepsizes of 16. But the values have just been copied from the orignal matrix without any summation. I think there is more simple solution to this but I can't seem to get it to work. Any help would be much appreciated.

Thanks in advance.

[KSSV]

You are calling sum on a single number.....how you expect sum?

Answer 1

[Andrei Bobrov]

Let A - your array [5000x6482]

d = 16;

ii = rem((0:size(A,1)-1)',d)+1;
[x,y] = ndgrid(ii,1:size(A,2));
out = accumarray([x(:),y(:)],A(:));