numpy.tril_indices(n, k=0, m=None)
[source]
Return the indices for the lower-triangle of an (n, m) array.
Parameters: |
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Returns: |
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See also
triu_indices
mask_indices
New in version 1.4.0.
Compute two different sets of indices to access 4x4 arrays, one for the lower triangular part starting at the main diagonal, and one starting two diagonals further right:
>>> il1 = np.tril_indices(4) >>> il2 = np.tril_indices(4, 2)
Here is how they can be used with a sample 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]])
Both for indexing:
>>> a[il1] array([ 0, 4, 5, ..., 13, 14, 15])
And for assigning values:
>>> a[il1] = -1 >>> a array([[-1, 1, 2, 3], [-1, -1, 6, 7], [-1, -1, -1, 11], [-1, -1, -1, -1]])
These cover almost the whole array (two diagonals right of the main one):
>>> a[il2] = -10 >>> a array([[-10, -10, -10, 3], [-10, -10, -10, -10], [-10, -10, -10, -10], [-10, -10, -10, -10]])
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https://docs.scipy.org/doc/numpy-1.17.0/reference/generated/numpy.tril_indices.html