MATLAB: How to sum some columns of a matrix

MATLABmatrixsum

Hi,
I am trying to add values in a matrix that each is identified as I(x,y).
What I need to do is to sum some columns and put them into a new matrix. For example, I want to add I(x1,y1)+I(x1,y2)+I(x1,y3) and put it in first column first row of the new matrix. Then add I(x2,y1)+I(x2,y2)+I(x2,y3) and put this value on the first column second row of the new matrix while keeping the other columns of the matrix the same… and so on.
For example:
      A=[1 2 3 4; 5 6 7 8; 9 10 11 12; 13 14 15 16];
      % sum columns 2 and 3 in B
      % B=[1 5 4; 5 13 8; 9 21 12; 13 29 16]
Can anyone help me with this please?
All the best Alvaro

Best Answer

A=[1 2 3 4; 5 6 7 8; 9 10 11 12; 13 14 15 16];
B = [A(:,1) sum(A(:,[2 3]),2) A(:,4)]
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