Need of a nested loop:

How would we sum each individual column, rather than getting an overall sum?

Answer:

The programming technique would need a nested loop in which the outer loop is over the columns. For illustration, we will modify the earlier function to sum each column and return a row vector containing the results.

Note: The output argument will be a row vector containing similar number of columns as the input argument matrix

Also, as the function is computing a sum for each column the runsum variable should be initialized to 0 for every column. Therefore it is initialized inside of the outer loop.

>> mat = [3:5; 2 5 7]

mat =

    3   4   5

    2   5   7

>> matcolsum(mat)

ans =

    5   9   12

Obviously, the built-in sum function in a MATLAB would accomplish similar thing.