* add support for __get_item__ of Variable test=develop

* update the infer shape of matmul,  test=release/1.6

* add unittests of matmul, test=release/1.6

* change func names, test=release/1.6

* test=develop, communicator_is_sgd_optimizer flags

【cherry-pick】 fix fill_constant shape with -1 and enhance cross_entropy test=release/1.6 (#20722) (#20728)

test=release/1.6

* - Flushing mkl-dnn cache

test=develop

- Disabled clearing cache for LoadModel

- Added clearing of mkl-dnn cache when Executor is created

test=develop

- Do not clear for GPU places

test=develop

- compilation fix

test=develop

* - Moved clearing of mkl-dnn cache in destructor of executor

test=develop

* - Compilation fix

test=develop

- Reverted conditional clearing of mkl-dnn cache in Executors's
  destructor

test=develop

- compilation fix

* fix op log bug, test=release/1.6

* add unittests, test=release/1.6

* Fix communicator slow bug & fix communicator stop bug (#20366)

* test=develop,Fix communicator slow bug

* test=develop, delete if() in stop_worker()

* test=develop

* fix UT, test=develop

* fix bug in fetch handler, test=develop

* fix bug in fetch handler, test=develop

* test=develop, fix fetch barrier bug

* test=develop, bug fix

* test=develop, bug fix

* test=develop, fix bug

* test=develop,test=release/1.6

* add condition judgement for performance improvement test=develop

* add condition judgement for performance improvement test=develop

* refine code style test=develop

test=develop
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

* Support fp16 in fused_elemwise_activation_op.
* Fix unit testing in ONLY-CPU mode.

* bug fix: invalid learning rate decay in pserver async mode

* add input type and dtype check, enhance shape error message for concat_op (#20101)

* add input type and dtype check, enhance shape error message for concat_op
test=develop

* enhance shape check
test=develop

* improve coverage

test=develop

* enhance input type chec for concat (#20584)

test=develop

* add expand_as op, test=develop

* add expand_as op,test=develop

* add expand_as op,test=develop

* add nn.py, test=develop

* delele paddle_enforce, test=develop

* add data type check, test=develop

* polish error messages, test=develop

* polish error messages, test=develop

* Remove support for the CPU architecture matmul, test=develop

* fix syntax bug, test=develop

* modified group_norm's unittest for pass statement, test=develop

* fix group_norm's bug: scale or bias is None which causes segmentation fault, test=develop

fix conv_transpose's bug: compatible with Anylayout setting: cherry-pick 20589

* fix recurrent bug
test=develop

* Fix while op bug
test=release/1.6

* add unit test
test=release/1.6

* Add seq2seq api related code (#19820)

* fix expand bug  (#20340)

* fix expand bug test=develop

* fix style test=develop

* fix style test=develop

* fix style test=develop

* fix style test=develop

* Fix the assign data check (#20564)

* Fix the assign data check. test=develop

* Fix test_assign_op.py. test=develop

* Update API.spec

Refine error message of transpose. fix en doc about unsqueeze, unstack, transpose, multiplex. test=develop, test=document_preview, test=document_fix (#20594)

* support reshape doubel grad, test=develop

* fix reshape double grad, pass converage, test=develop

* fix review, test=develop

1. fill_constant support Tensor;
2. fix bug in backward.py: using fill_constant instead of fill_constant_batch_size_like
3. fix bug in ExpandGradOp.
test=release/1.6 (#20521)

* Add input check and refine error message

* Refine test case and comments

test=develop
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

* fix_conv_grad_grad

* fix_bug, test=develop

* fix error message for elementwise_add/mul;test=develop

* edit error message;test=develop

* add input type and dtype check for accuracy_op

* add input type and dtype check for accuracy_op

* modify python error on accuracy_op,add test=develop

* modify details on accuracy_op, test=develop

* test float16, test=develop

* add warning, test=develop

Fix api doc example bug and polish square doc (#20491)

test=develop
test=document_fix

* Refine topk stack squeeze api en doc

test=develop
test=document_fix

* refine api.spec and returns

test=develop
test=document_fix
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

test=develop, test=release/1.6, test=document_fix

* refine eng doc for hard_sigmoid op
test=develop
test=document_fix

* refine the description of hard_sigmoid
 test=develop
test=document_fix

* update API.spec
test=document_fix

* Refine the decription of parameters of HardSigmoid op
test=develop, test=document_fix

* Update API.spec for hard_sigmoid op
test=develop, test=document_fix

* fix elementwise floordiv mod; test=develop

* restore nn.py; test=release/1.6

* change floordiv, mod  doc; test=release/1.6

* fix APIs: relu, relu6, hash

test=develop
test=document_fix

* fix relu6 doc

test=develop
test=document_fix

* fix API.spec

test=develop
test=document_fix

* add description link for hash

test=develop
test=document_fix

* fix API:cos, exp, ceil, elu, brelu English doc
test=develop
test=document_fix