# numpy.diag_indices¶

numpy.diag_indices(n, ndim=2)[source]

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.

Notes

New in version 1.4.0.

Examples

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=np.int)
>>> a[d3] = 1
>>> a
array([[[1, 0],
[0, 0]],
[[0, 0],
[0, 1]]])
```

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