numpy如何计算差分和累计和？

#计算差分 a = np.array([1,2,3,4,5,6,7]) np.diff(a) out:array([1, 1, 1, 1, 1, 1]) #计算累积和 b = np.array([1,2,3,4,5,6,7,8]) b.cumsum() out:array([ 1, 3, 6, 10, 15, 21, 28, 36])