MATLAB: Why is this summation not working properly?

Question

I'm trying to perform a really simple summation in MATLAB. Here is my code:

moment = 0;

for y=1:rows,
    for x=1:cols,
        moment = moment + (x^p * y^q * Im(y,x));
    end
end

I want (x^p * y^q * Im(y,x)) to be calculated for each iteration and added to the moment variable, but this function is returning the moment the first time it's calculated. It doesn't seem to do the adding at all.

Probably a stupid mistake, but I am really confused. Any suggestions?

Answer 1

Could it be that Im is of type uint8 or some similar type of small range? Try putting this line before the loops:

Im = double(Im);

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BTW you can rewrite your code in one line:

moment = sum(sum( ((1:rows)'.^q * (1:cols).^p) .* double(Im) ));

Answer 2

put a breakpoint on the moment = moment + ... line and see if the variable "moment" is being increased.

I'm not sure why you use the comma in the for statement. It shouldn't have an effect, I don't think, but it's unnecessary.