Walk through your code, line by line. How many times does MATLAB execute the body of your while loop?
I think you want to iterate while the two variables are not equal, breaking out of the loop when they are equal.
You also never define the variable somma that you display on the line with the %1 comment.
Image Analyst's point about your variable names is a good one. If you want to clearly indicate that they are your candidate sums, perhaps use variable names like sumPrevious and sumCurrent.