* reimplement pow operator

* add pow_grad operator

* fix code style

* fix build error

* fix op_test bug

* revert pow operator

* add FIXME comment

* remove unused code

* fix cmake file

* fix build error

* improve unique_name, uniq id is related to prefix

* fix join

* add logs and fix a bug

* fix break buf

* modify path bugs

* fix by comments

* fix by comments

* add batch

* add float32tostring

* add pb support

* moidfy gotpaht

* compile ok

* add proto

* delete not need

* add proto

* add empty proto

* clean not need

* clean not need

* modify deps

* fix by comments and update depend

* fix compile error

* fix loop bugs

* "add sequence conv layer"

* "add sequence layer"

* add networks

* "fix based comment"

* Update layers.py

* Fix Type error

* Fix error

* Fix top_k_op GPU code data type

Update CONTRIBUTION.md to generate correctly on SPHINX

* add resnet

* optimize code

* Add symbolic link from Paddle/CONTRIBUTING.md to doc/howto/dev/contribute_to_paddle_en.md so sphinx can generate the document
* Update CONTRIBUTING.md links so sphinx does not add these links to the TOC
* Removed dev/contribute_to_paddle_cn.md from documentation, since this document is not in sync with Paddle/CONTRIBUTING.md

* add init_gflags interface

* refine code

* follow comments

* Create vlog_guide.md

* Move design/vlog_guide.md into CONTRIBUTE.md

* In response to comments from Yu Yang and Tony

* In response to comments from Luo Tao

* Fix Type error

* Fix error

fix_sequence_conv_op

Seq expand op

2. Fix comments and paddle enforce check

fix pool op

* add batch_norm_layer

* add img_conv_group layer and test

* add check to Tensor.type()

* forward can run

* with backward

* change label data time from int32 to int64

* refine code

* follow comment

Feature/multigpu

* Cast Operator

Cast input variable to other data type

* Fix compile error

* Add cast op

* Follow comments

* Accuracy does not support float/double, only support integers
* Polish error message when an operator does not support some device.

* add sparse support for sum op

* typo fix

* fix gpu build error

* fix unittest error

* typo fix

* infer var type and shape in op_test

* follow comments

* fix build error

* bypass some unittests depend on NetOp

* support sparse output for lookup table grad op

* refine codes

* fix gpu build error

* fix lookup table grad gpu kernel

* fix ci

* fix ci

* fix ci

* fix bug in lookup_table_grad op

* fix bug in test_word2vec

* register double kernel for some operators

* set is_sparse=True in test_word2vec

* fix lookup table grad op CUDA kernel bug

* disable test_modified_huber_loss_op temporarily

* disable test_lstm_unit_op temporarily

* Shrink Operator.h

* Fix CI compile

* Adding the increment op for global step

* Changing list to single op as per code review feedback

* Add `dump_to_file()` for ProgrameDescBind in pybind

* Update

* Add utility.py

* typo

* Fix bugs

* Move add_feed/fetch_components to untility.py

* Compelete dump

* Follow comments

* Change output of Prune() from inference to pointer

* Expose Prune() to Python

* Compelete save/load API of inference model

* Fix errors

* Debuging

* Compelete unit tests

* follow comments

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