which one is the correct procedure for 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

Answer 1

[Walter Roberson]

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.