How to sum specific elements in a row of a matrix

I have a 256 by 256 matrix, lets say it is called m.

I would like to sum specific elements from a specific row in that matrix.

For example, just looking at row 1, I would like to sum the following of these elements:

1-4, (multiples of 16) + 1, (multiples of 16) + 2, (multiples of 16) + 3, and (multiples of 16) + 4.

Therefore I will end up with a single value for each row of the matrix.

Please can somebody help me with the coding for this?

Thank you

Answer 1

[Ameer Hamza]

Try this:

m = rand(256,256);
mask = reshape((1:16:256)+(0:3)', 1, []);
result = sum(m(:,mask), 2);

[Ashton Linney]

That is absolutely perfect! Thank you Ameer!

Answer 2

[darova]

try this

A = rand(256);
srow = 0;
for i = 1:16:size(A,1)
    srow = srow + sum(A(i:i+3,:),1);
end