This is a great example of where vectorization would be the best way to get this result. Most inbuilt MATLAB functions can operate on whole arrays at once, without requiring any loops: this is much faster to run, and the code required is much neater too! Using vectorized code is also much more expandable than using loops, so even if the data gets much larger, it will still be the fastest and most optimal way to calculate.
>> D = [1 2 3; 4 5 6];
>> sum(D,2)
ans =
6
15
And there is your result! Note that this uses sum's optional second input to specify which dimension we want to sum along.
Of course if you are writing your own functions then you can (and should) consider writing them to perform operations completely vectorized. Keep this in mind: in MATLAB loops are the second choice, not the first!
