SVD docs improved (#54002)
Summary:
- Corrected a few errata in the SVD docs
- Made the notation more uniform (refer to `Vh` in `linalg.svd`, always use double tilts...)
- Wrote a better explanation about why the gradients of `U` and `V` are not well-defined when the input is complex or real but has repeated singular values. The previous one pointed to a somewhat obscure post on gauge theory.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54002
Reviewed By: malfet
Differential Revision: D27459502
Pulled By: mruberry
fbshipit-source-id: f5c35eca02d35dadd2fc0eeadfacc8824f409400
