Corrected typo in Cross entropy formula (#70220)
Summary:
Changes made to line 1073: The denominator of the formula was the EXP(SUM(x)) and changed it to SUM(EXP(x))
Fixes #ISSUE_NUMBER
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70220
Reviewed By: davidberard98
Differential Revision: D33279050
Pulled By: jbschlosser
fbshipit-source-id: 3e13aff5879240770e0cf2e047e7ef077784eb9c
