* Enable BatchNorm to use global mean and variane during training
* Update doc and follow comments.

* add doc for scope

* update doc for force_init_on_cpu
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* follow comment test=develop

* update format test=develop

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* optimize bilinear_tensor_product
* add set zero to set grad to 0.

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* Fix truncated normal.

* Fix.

* Make nce support more distribution.

* Fix API.spec.

* Fix python API.

* Fix.
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* Fix API.spec
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* Fix sampler.

* Fix order of arguments in python API.
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* NCE add selectedrows support

* NCE update weighted sampling

* fix bugs in nce_op, and assign_value_op optimized

* fix bugs in nce_op, revert assign_value_op

* nce_op optimize

* nce_op optimize

* nce_op optimize

* add selectedRows test later

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* add selectedRows supported

* add selectedRows supported

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* add selectedRows supported

* add nce selectedRows supported, test=develop

* add nce selectedRows supported

* add nce selectedRows supported, test=develop

* fix height in nce, test=develop

* add ut

* add ut, test=develop

* make AutoGrownIndex inline
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* fix tinny error, test=develop

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