flatten, flatten2, gather, gather_nd, group_norm, gru,
gru_unit, reduce_max, reduce_min, reduce_mean, reduce_sum,
reshape, scatter_nd_add, sequence_expand, sequence_expand_as,
sequence_pad

* append optimize op in the grad block of current block if current block is in control flow. test=develop

* add conditional grad op when optimizer used in control flow. test=develop

* add comment and modify typo. test=develop

* fix append_backward to support control flow. test=develop

* add test. test=develop

* fix copy_var_to_parent_block and conditional_block_grad. test=develop

* fix bug: revert to append conditional_block_grad vars to sub grad block. test=develop

* fix bug: revert to assign var to parent block even if var already is in parent block

* fix bug: consider outputs is empty. test=develop

* move _rename_grad_ out. test=develop

* modify code according to reviews from Huihuang. test=develop

* modify code according to reviews from Jinle. test=develop

* fix test_conv2d_ngraph for grad diff, test=develop

* register NoNeedBufferVarsInference for max_pool_grad_op, test=develop

* refine error message, test=develop

* fix numpy, test=develop

* disable test conv2d_ngraph_op, test=develop
Co-authored-by: NZhang Ting <709968123@qq.com>

* test=develop fix generate_proposal_labesl op

* convert dtype of vars for range op, test=develop

fix unittest for spp op

* move private weight properties to public ones
test=develop

* revert changes to FC
test=develop

* fix unittest
test=develop

* fix unittest
test=develop

* fix coverage
test=develop

* fix merged dev
test=develop

* bug fix
test=develop

* update doc, test=develop

* fix related unittests, test=develop

* fix str incompatible error, test=develop

* add is_empty_grad_op for OpTest, test=develop

* expost fluid.dygraph.TracedLayer apis, test=develop

* polish doc, test=develop

* follow comments, test=develop, test=document_fix

* follow comments, test=develop

* remove save_inference_model return value, test=develop

* enhance checking validity of apply_gradient test=develop

* refactor code test=develop

* stash

* add adamOptimizer test=develop

* add adamOptimizer test=develop

* update layers used in mnist dygraph model, test=develop

* fix import issue, test=develop

* add dygraph utils, test=develop

* add unittest, test=develop

* test=develop add fp64 check_grad for conv2d, conv3d

* fix no grad check for pool_max & spectral_norm. test=develop

* use large input size in test_add_position_encoding_op.py, test=develop

* revert shape_white_list, test=develop

* add shuffle batch op, test=develop, test=document_preview

* fix size_t conflict and check_output test=develop, test=document_preview

* fix bug test=develop, test=document_preview

* add unittest of shuffle_batch layer test=develop, test=document_preview

* fix py coverage and op input type, test=develop, test=document_preview

* fix py coverage, test=develop

* fix en doc, test=develop

* move to contrib test=develop

* add unique_name test=develop

* invoke shuffle_batch in contrib.layers test=develop

* remove params in Tracer object, test=develop

* Repair failed optest, test=develop

* remove build_once & name_scope (Conv2D)
test=develop

* fix unittest
test=develop

* Conv2DTranspose

* Conv3D & Conv3DTranspose
test=develop

* Pool2D & BatchNorm

* Embedding

* LayerNorm

* GRUUnit & NCE

* PRelu

* BilinearTensorProduct

* GroupNorm & SpectralNorm

* TreeConv
test=develop

* fix LayerNorm in transformer unnittest
test=develop

* disable LayerNorm or BatchNorm in multicard
test=develop

* refine Layer.create_parameter api
test=develop

* refine LayerNorm, remove begin_norm_axis param, add normed shape check
test=develop

* LayerNorm bug fix
test=develop

* fix optest,test=develop

* fix optest, test=develop

* fix optest for pass parameter_list when constructing an Optimizer class instance, test=develop

* polish code for better code style, test=develop

* fix se_resnext optest, test=develop

* polish code for better code style, test=develop
Co-authored-by: Nsongyouwei <youwei0314@gmail.com>

* make reverse op support negative axis

* test=develop

* test=develop

* test=develop

* change the check_shape_white_list in web

* test=develop

* test=develop

* fix stat shape back in global auc scenario
* add UT to cover global auc

* add ParameterList container

* add unittest
test=develop

* fix container, rebase remove build_once
test=develop

* add parameters None check
test=develop

* update Sequential unittest
test=develop

* use Linear in Sequential sample code
test=develop

* fix Sequential arg type doc
test=develop

* move sequence op unittests to a separate folder
test=develop

* add missing CMakeList file
test=develop

* fix relative path import
test=develop

* fix relative import
test=develop

* use sys.path.append
test=develop

* optimize adam speed by removing _finish_update test=develop

* fix SparseAdamFunctor param list test=develop

* Remove scale_op in expect_list of adam_op test=develop

* fix test optimizer loss assert error test=develop

* fix test optimizer loss assert error test=develop

* modify PADDLE_ENFORCE usage test=develop

* fix op_type in lamb_op.cc test=develop

* fix errors ostream format bug test=develop

* add betaPowOut in ngraph op test=develop

* fix ngraph::op api for gcc8 test=develop

* clean code test=develop

* modify struct into class test=develop

* remove code of beta1Tensor in lamb_op test=develop