numpy 1: np.cumsum()

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a = np.array([[1,2,3], [4,5,6]])
a
array([[1, 2, 3],
[4, 5, 6]])
np.cumsum(a)
array([ 1, 3, 6, 10, 15, 21])
np.cumsum(a, dtype=float) # specifies type of output value(s)
array([ 1., 3., 6., 10., 15., 21.])
np.cumsum(a,axis=0) # sum over rows for each of the 3 columns
array([[1, 2, 3],
[5, 7, 9]])
np.cumsum(a,axis=1) # sum over columns for each of the 2 rows
array([[ 1, 3, 6],
[ 4, 9, 15]])