pytorch

1f3807ce - More stable and faster implementation of the gradient of torch.linalg.eigh (#55049)

More stable and faster implementation of the gradient of torch.linalg.eigh (#55049) Summary: This PR: - Renames symeig_backward to eigh_backward - Improves the stability and speed of the gradient computation by doing `V(A + B)Vh` instead of `VAVh + VBVh` when both the gradients of the eigenvectors and eigenvalues are defined. - Updates the comments of the function to make them arguably clearer Pull Request resolved: https://github.com/pytorch/pytorch/pull/55049 Reviewed By: ngimel Differential Revision: D28396823 Pulled By: mruberry fbshipit-source-id: a144482bfb1054e281b58ae1fe3cf1015bab505d