Adds missing abs to lcm (#41552)
Summary:
lcm was missing an abs. This adds it plus extends the test for NumPy compliance. Also includes a few doc fixes.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41552
Reviewed By: ngimel
Differential Revision: D22580997
Pulled By: mruberry
fbshipit-source-id: 5ce1db56f88df4355427e1b682fcf8877458ff4e
