numpy.fill_diagonal(a, val, wrap=False)
[source]
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]
all identical. This function modifies the input array in-place, it does not return a value.
Parameters: |
|
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See also
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.
>>> a = np.zeros((3, 3), int) >>> np.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 = np.zeros((3, 3, 3, 3), int) >>> np.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]])
The wrap option affects only tall matrices:
>>> # tall matrices no wrap >>> a = np.zeros((5, 3), int) >>> np.fill_diagonal(a, 4) >>> a array([[4, 0, 0], [0, 4, 0], [0, 0, 4], [0, 0, 0], [0, 0, 0]])
>>> # tall matrices wrap >>> a = np.zeros((5, 3), int) >>> np.fill_diagonal(a, 4, wrap=True) >>> a array([[4, 0, 0], [0, 4, 0], [0, 0, 4], [0, 0, 0], [4, 0, 0]])
>>> # wide matrices >>> a = np.zeros((3, 5), int) >>> np.fill_diagonal(a, 4, wrap=True) >>> a array([[4, 0, 0, 0, 0], [0, 4, 0, 0, 0], [0, 0, 4, 0, 0]])
The anti-diagonal can be filled by reversing the order of elements using either numpy.flipud
or numpy.fliplr
.
>>> a = np.zeros((3, 3), int); >>> np.fill_diagonal(np.fliplr(a), [1,2,3]) # Horizontal flip >>> a array([[0, 0, 1], [0, 2, 0], [3, 0, 0]]) >>> np.fill_diagonal(np.flipud(a), [1,2,3]) # Vertical flip >>> a array([[0, 0, 3], [0, 2, 0], [1, 0, 0]])
Note that the order in which the diagonal is filled varies depending on the flip function.
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https://docs.scipy.org/doc/numpy-1.17.0/reference/generated/numpy.fill_diagonal.html