above the `k`-th diagonal zeroed.
For arrays with ``ndim`` exceeding 2, `tril` will apply to the final two
axes.

Parameters
----------
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.

Returns
-------
tril : ndarray, 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]]])

é