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Module « numpy.matlib »

Fonction diag_indices - module numpy.matlib

Signature de la fonction diag_indices

def diag_indices(n, ndim=2) 

Description

help(numpy.matlib.diag_indices)

Return the indices to access the main diagonal of an array.

This returns a tuple of indices that can be used to access the main
diagonal of an array `a` with ``a.ndim >= 2`` dimensions and shape
(n, n, ..., n). For ``a.ndim = 2`` this is the usual diagonal, for
``a.ndim > 2`` this is the set of indices to access ``a[i, i, ..., i]``
for ``i = [0..n-1]``.

Parameters
----------
n : int
  The size, along each dimension, of the arrays for which the returned
  indices can be used.

ndim : int, optional
  The number of dimensions.

See Also
--------
diag_indices_from

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

Create a set of indices to access the diagonal of a (4, 4) array:

>>> di = np.diag_indices(4)
>>> di
(array([0, 1, 2, 3]), array([0, 1, 2, 3]))
>>> 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]])
>>> a[di] = 100
>>> a
array([[100,   1,   2,   3],
       [  4, 100,   6,   7],
       [  8,   9, 100,  11],
       [ 12,  13,  14, 100]])

Now, we create indices to manipulate a 3-D array:

>>> d3 = np.diag_indices(2, 3)
>>> d3
(array([0, 1]), array([0, 1]), array([0, 1]))

And use it to set the diagonal of an array of zeros to 1:

>>> a = np.zeros((2, 2, 2), dtype=int)
>>> a[d3] = 1
>>> a
array([[[1, 0],
        [0, 0]],
       [[0, 0],
        [0, 1]]])

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