MATLAB: Specifying the iteration range for ‘for’ loops

for loop

Say I have a matrix of size 5-by-5. I want to sum the elements in the rows, but I don't want to sum from the first column all the time, I want to choose from which column to sum from for any row. So say first row I want to sum 2:5, 2nd row 1:5, 3rd row 4:5, etc. How do I do this?

Best Answer

There is no need to use a loop:
>> M = randi(9,5,5) % random 5x5 matrix
M =
   7   1   5   6   6
   7   4   8   2   5
   7   4   4   1   7
   7   3   7   6   4
   8   8   6   9   1
>> V = [2,1,4,4,3]; % first column
>> X = bsxfun(@ge,1:5,V(:))
X =
   0   1   1   1   1
   1   1   1   1   1
   0   0   0   1   1
   0   0   0   1   1
   0   0   1   1   1
>> sum(M.*X,2)
ans =
   18
   26
    8
   10
   16
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