* add ignore index

* update api.spec

* enhance softmax_with_cross_entropy

* Add intermediate

* fix flatten/squeeze/unsqueeze

* Considering compatibility issues, we could not fix the origin op

* follow comment

* reset the shape of XShape

* Add pad2d op.

* Add unitest and python api.

* Fix cuda op kernel.

* Fix python api.

* Fix python api.

* Update API.spec.

* Fix python api

* enhance pad_constant_like_op

* add API

* add API

This reverts commit f5d5d7b2.

* Disable in_place in batch_norm API.

* Fix scatter_op python API and remove inconsistency between implementation and doc

* API spec change

* Change as review comment

* Add three modes for prelu_op.

Add flatten op interface and enhance APIs about detection to support variable-length image. (#12422)

* add flatten api&enhance detection api

* unify shape_op data type

* update API.spec

Fix str and bytes problem
Fix sorted problem
Fix math problem
Fix CI problem

* fix the result of unit test

* fix resnext

* compare the result of PE and Exe

* compare the result of reduce and allreduce

* "remove inplace in single op"

* "fix ci"

* "add transpiler case"

* fix conflict

* "fix reshape"

* "delete reshape inplace attr"

* "follo the comments"

* "rerun ci"

* expose rank_loss python api

* Fix serious bug in nesterov momentum optimizer.

* remove block api

* remove clone_variable

* hide block inner apis

* update

* fix tests