doc fix for lu pivots + more info

torch/functional.py

@@ -1449,7 +1449,12 @@ def _lu_impl(A, pivot=True, get_infos=False, out=None):
 
             - **factorization** (*Tensor*): the factorization of size :math:`(*, m, n)`
 
-            - **pivots** (*IntTensor*): the pivots of size :math:`(*, m)`
+            - **pivots** (*IntTensor*): the pivots of size :math:`(*, \text{min}(m, n))`.
+              ``pivots`` stores all the intermediate transpositions of rows.
+              The final permutation ``perm`` could be reconstructed by
+              applying ``swap(perm[i], perm[pivots[i] - 1])`` for ``i = 0, ..., pivots.size(-1) - 1``,
+              where ``perm`` is initially the identity permutation of :math:`m` elements
+              (essentially this is what :func:`torch.lu_unpack` is doing).
 
             - **infos** (*IntTensor*, *optional*): if :attr:`get_infos` is ``True``, this is a tensor of
               size :math:`(*)` where non-zero values indicate whether factorization for the matrix or