numpy.tril

numpy.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.

Parameters:

marray_like, shape (…, M, N)

Input array.

kint, 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.

Returns:

trilndarray, shape (…, M, N)

Lower triangle of m, of same shape and data-type as m.

See also

triu

same thing, only for the upper triangle

Examples

>>> import numpy as np
>>> np.tril([[1,2,3],[4,5,6],[7,8,9],[10,11,12]], -1)
array([[ 0,  0,  0],
       [ 4,  0,  0],
       [ 7,  8,  0],
       [10, 11, 12]])

>>> np.tril(np.arange(3*4*5).reshape(3, 4, 5))
array([[[ 0,  0,  0,  0,  0],
        [ 5,  6,  0,  0,  0],
        [10, 11, 12,  0,  0],
        [15, 16, 17, 18,  0]],
       [[20,  0,  0,  0,  0],
        [25, 26,  0,  0,  0],
        [30, 31, 32,  0,  0],
        [35, 36, 37, 38,  0]],
       [[40,  0,  0,  0,  0],
        [45, 46,  0,  0,  0],
        [50, 51, 52,  0,  0],
        [55, 56, 57, 58,  0]]])