`numpy:tril`

Signature

def tril ( m , k = 0 )

Lower triangle of an array.

Return a copy of an array with elements above the k-th diagonal zeroed. For arrays with ndim exceeding 2, tril will apply to the final two axes.

m : array_like, shape (..., M, N): Input array.
k : int, optional: Diagonal above which to zero elements. k = 0 (the default) is the main diagonal, k < 0 is below it and k > 0 is above.

tril : ndarray, shape (..., M, N): Lower triangle of m, of same shape and data-type as m.

import numpy as np
np.tril([[1,2,3],[4,5,6],[7,8,9],[10,11,12]], -1)

✓

np.tril(np.arange(3*4*5).reshape(3, 4, 5))

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