# numpy.fill_diagonal¶

numpy.fill_diagonal(a, val)

Fill the main diagonal of the given array of any dimensionality.

For an array a with a.ndim > 2, the diagonal is the list of locations with indices a[i, i, ..., i] all identical. This function modifies the input array in-place, it does not return a value.

Parameters: a : array, at least 2-D. Array whose diagonal is to be filled, it gets modified in-place. val : scalar Value to be written on the diagonal, its type must be compatible with that of the array a.

Notes

New in version 1.4.0.

This functionality can be obtained via diag_indices, but internally this version uses a much faster implementation that never constructs the indices and uses simple slicing.

Examples

```>>> a = zeros((3, 3), int)
>>> fill_diagonal(a, 5)
>>> a
array([[5, 0, 0],
[0, 5, 0],
[0, 0, 5]])
```

The same function can operate on a 4-D array:

```>>> a = zeros((3, 3, 3, 3), int)
>>> fill_diagonal(a, 4)
```

We only show a few blocks for clarity:

```>>> a[0, 0]
array([[4, 0, 0],
[0, 0, 0],
[0, 0, 0]])
>>> a[1, 1]
array([[0, 0, 0],
[0, 4, 0],
[0, 0, 0]])
>>> a[2, 2]
array([[0, 0, 0],
[0, 0, 0],
[0, 0, 4]])
```

#### Next topic

numpy.ndenumerate