* add double grad compute for batch norm,test=develop

* fix unittest, test=develop

* remove unuse tensor,test=develop

* add format,test=develop

* update, test=develop

and optimize the c++ implmentation of empty op as PR#26659 reviews,
and add bool for shape op.

* enhance collect_op for dygraph, test=develop

* enhance detection ops with lod, test=develop

* support none bbox left in generate_proposals, test=develop

* unfiy MultiLevelRoisNum, test=develop

* update core.ops, test=develop

* add op register for new input & output, test=develop

* delate some wrong message test=develop, test=document_fix

* delate some wrong message

* fix unsqueeze in dygraph

* add test

* add test

update doc of paddle.to_tensor

* refine paddle.stack

* support TensorArray

* add test

* fix coverage problem

* fix coverage problem

* fix sample code

As the title

* add embedding 2.0

* add embedding support input int32

* set default dtype for distribution API

* Add unittest

* Add unittest

* fix import get_default_dtype problem

* delete change under fluid.layers.nn

* little change

* add deprecated, test=develop

add broadcast feature for elementwise logical op

* update doc, test=document_fix

* add attr(dtype)

* refine code

As the title.
Co-authored-by: Nwujionghao <wujionghao@email.com>

* add static data

* add matmul_v2

* [API2.0] add dropout, dropout2d and dropout3d, test=develop

* refine Interface and assertion after review, test=develop

* fix alias p=1 and use scale, test=develop

* fix doc and training, test=develop

* fix doc in Dropout2D, test=develop

* Update `paddle.clamp`

rename to `paddle.clip`
add fast path for dygraph mode
remove `out`
rename `input` -> `x`
update doc sample

* Fix leftover `Variable` wording

* Indent doc with spaces

* Remove `:alias` in docs

* Update `enable_imperative` -> `disable_static`

* Remove `imperative`

also trigger CI

* Update tests for better coverage

* Rebase to fix `cosine_similarity`

* Fix `cosine_similarity` some more

* Add new API: paddle.prod

test=develop

(1) Add api paddle.reshape(x, shape, name); 

(2) Use Tensor replaces Variable. test=develop