MATLAB: Which one is the correct procedure for summation

summation

I want to implement the following equation
Kindly tell me,which method is correct
ID =0;
for i=1:256
ID = ID+HD(i);
end
or otherwise
   ID = sum(HD(1:256))
Please help me

Best Answer

ID = sum(HD(1:256)) is faster.
If you were summing large enough arrays then there could be difference in the output due to round off differences when the large summation was handed over to fast routines that use multiple threads to create partial sums that are then added together.
Related Question