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Module « numpy.matlib »

Fonction tril_indices_from - module numpy.matlib

Signature de la fonction tril_indices_from

def tril_indices_from(arr, k=0) 

Description

help(numpy.matlib.tril_indices_from)

Return the indices for the lower-triangle of arr.

See `tril_indices` for full details.

Parameters
----------
arr : array_like
    The indices will be valid for square arrays whose dimensions are
    the same as arr.
k : int, optional
    Diagonal offset (see `tril` for details).

Examples
--------
>>> import numpy as np

Create a 4 by 4 array

>>> a = np.arange(16).reshape(4, 4)
>>> a
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11],
       [12, 13, 14, 15]])

Pass the array to get the indices of the lower triangular elements.

>>> trili = np.tril_indices_from(a)
>>> trili
(array([0, 1, 1, 2, 2, 2, 3, 3, 3, 3]), array([0, 0, 1, 0, 1, 2, 0, 1, 2, 3]))

>>> a[trili]
array([ 0,  4,  5,  8,  9, 10, 12, 13, 14, 15])

This is syntactic sugar for tril_indices().

>>> np.tril_indices(a.shape[0])
(array([0, 1, 1, 2, 2, 2, 3, 3, 3, 3]), array([0, 0, 1, 0, 1, 2, 0, 1, 2, 3]))

Use the `k` parameter to return the indices for the lower triangular array
up to the k-th diagonal.

>>> trili1 = np.tril_indices_from(a, k=1)
>>> a[trili1]
array([ 0,  1,  4,  5,  6,  8,  9, 10, 11, 12, 13, 14, 15])

See Also
--------
tril_indices, tril, triu_indices_from

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