Return the indices for the lower-triangle of arr.

This docstring was copied from numpy.tril_indices_from.

Some inconsistencies with the Dask version may exist.

See tril_indices for full details.

Parameters
arrarray_like

The indices will be valid for square arrays whose dimensions are the same as arr.

kint, optional

Diagonal offset (see tril for details).

Notes

New in version 1.4.0.

Examples

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])
```