>>> x = np.arange(9)
>>> x
array([0, 1, 2, 3, 4, 5, 6, 7, 8])
>>> np.sum(x)
36
>>> x = x.reshape(3,3)
>>> np.sum(x)
36
>>> x
array([[0, 1, 2],
[3, 4, 5],
[6, 7, 8]])
>>> x.sum(axis=0)
array([ 9, 12, 15])
>>> x.sum(axis=1)
array([ 3, 12, 21])
Exercise:
Test the result of cumsum!