5.49.5 Cumulated sum of elements of each column of a matrix: cumSum
cumSum takes as argument a matrix A. cumSum returns the matrix whose columns are the cumulated sum of the
elements of the corresponding column of the matrix A.
Input:
cumSum([[1,2],[3,4],[5,6]])
Output:
[[1,2],[4,6],[9,12]]
since the cumulated sums are: 1, 1+3=4, 1+3+5=9 and 2, 2+4=6, 2+4+6=12.