np.triu

numpy.triu(m, k=0)
Upper triangle of an array.
Return a copy of a matrix with the elements below the k-th diagonal zeroed.

返回一个矩阵的上三角矩阵，第k条对角线以下的元素归零

例如：

import numpy as np
np.triu(np.ones([4,4]), k=1).astype('uint8')

output:

array([[0, 1, 1, 1],[0, 0, 1, 1],[0, 0, 0, 1],[0, 0, 0, 0]], dtype=uint8)

import numpy as np
np.triu(np.ones([4,4]), k=0).astype('uint8')

output:

array([[1, 1, 1, 1],[0, 1, 1, 1],[0, 0, 1, 1],[0, 0, 0, 1]], dtype=uint8)