Fix scalar check of MultiLabelMarginLoss. (#30768)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30768
The behavior didn't match the documentation, because the documentation (for 'none' reduction) reads:
input X target -> output
(N, C) X (N, C) -> (N,)
(C,) X (C,) -> ()
but the later case would output (1,). This also changes the case to:
() X (C,) -> ()
from:
() X (C,) -> (C,)
which makes more sense with the above formulas.
Restacked version of: https://github.com/pytorch/pytorch/pull/30748
Test Plan: Imported from OSS
Differential Revision: D18821554
Pulled By: gchanan
fbshipit-source-id: 3df77c51cf25648cb5fab62a68b09f49c91dab4e
