add fluid enable_imperative doc; test=develop (#2099)

doc/fluid/api/dygraph.rst

@@ -16,6 +16,7 @@ fluid.dygraph
     dygraph/CosineDecay.rst
     dygraph/DataParallel.rst
     dygraph/disable_dygraph.rst
+    dygraph/disable_imperative.rst
     dygraph/Dropout.rst
     dygraph/dygraph_to_static_code.rst
     dygraph/dygraph_to_static_func.rst
@@ -23,6 +24,7 @@ fluid.dygraph
     dygraph/dygraph_to_static_program.rst
     dygraph/Embedding.rst
     dygraph/enable_dygraph.rst
+    dygraph/enable_imperative.rst
     dygraph/enabled.rst
     dygraph/ExponentialDecay.rst
     dygraph/grad.rst

doc/fluid/api/dygraph/disable_imperative.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_fluid_dygraph_disable_imperative:
+
+disable_imperative
+------------------
+
+..  autofunction:: paddle.fluid.dygraph.disable_imperative
+    :noindex:
+

doc/fluid/api/dygraph/enable_imperative.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_fluid_dygraph_enable_imperative:
+
+enable_imperative
+-----------------
+
+..  autofunction:: paddle.fluid.dygraph.enable_imperative
+    :noindex:
+

doc/fluid/api/fluid.rst

@@ -23,10 +23,12 @@ fluid
     fluid/default_startup_program.rst
     fluid/device_guard.rst
     fluid/disable_dygraph.rst
+    fluid/disable_imperative.rst
     fluid/DistributeTranspiler.rst
     fluid/DistributeTranspilerConfig.rst
     fluid/embedding.rst
     fluid/enable_dygraph.rst
+    fluid/enable_imperative.rst
     fluid/ExecutionStrategy.rst
     fluid/Executor.rst
     fluid/get_flags.rst

doc/fluid/api/fluid/disable_imperative.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_fluid_disable_imperative:
+
+disable_imperative
+------------------
+
+..  autofunction:: paddle.fluid.disable_imperative
+    :noindex:
+

doc/fluid/api/fluid/enable_imperative.rst

+..  THIS FILE IS GENERATED BY `gen_doc.{py|sh}`
+    !DO NOT EDIT THIS FILE MANUALLY!
+
+.. _api_fluid_enable_imperative:
+
+enable_imperative
+-----------------
+
+..  autofunction:: paddle.fluid.enable_imperative
+    :noindex:
+

doc/fluid/api_cn/fluid_cn.rst

@@ -24,11 +24,13 @@ fluid
     fluid_cn/default_main_program_cn.rst
     fluid_cn/default_startup_program_cn.rst
     fluid_cn/disable_dygraph_cn.rst
+    fluid_cn/disable_imperative_cn.rst
     fluid_cn/device_guard_cn.rst
     fluid_cn/DistributeTranspiler_cn.rst
     fluid_cn/DistributeTranspilerConfig_cn.rst
     fluid_cn/embedding_cn.rst
     fluid_cn/enable_dygraph_cn.rst
+    fluid_cn/enable_imperative_cn.rst
     fluid_cn/ExecutionStrategy_cn.rst
     fluid_cn/Executor_cn.rst
     fluid_cn/get_flags_cn.rst

doc/fluid/api_cn/fluid_cn/disable_imperative_cn.rst

+.. _cn_api_fluid_disable_imperative:
+
+disable_imperative
+-------------------------------
+
+.. py:function:: paddle.fluid.disable_imperative()
+
+该接口退出动态图模式。
+
+返回：无
+
+**示例代码**
+
+.. code-block:: python
+
+    import paddle.fluid as fluid
+
+    fluid.enable_imperative()  # Now we are in imperative mode
+    x = fluid.layers.ones( (2, 2), "float32")
+    y = fluid.layers.zeros( (2, 2), "float32")
+    z = x + y
+    print( z.numpy() )   #[[1, 1], [1, 1]]
+    fluid.disable_imperative() # Now we are in declarative mode

doc/fluid/api_cn/fluid_cn/enable_imperative_cn.rst

+.. _cn_api_fluid_enable_imperative:
+
+enable_imperative
+-------------------------------
+
+.. py:function:: paddle.fluid.enable_imperative(place=None)
+
+该接口打开动态图模式。
+
+参数：
+  - **place** (fluid.CPUPlace 或 fluid.CUDAPlace，可选) - 执行动态图的设备。若为None，则设备根据paddle的编译方式决定。默认值为 ``None``。
+
+返回：无
+
+**示例代码**
+
+.. code-block:: python
+
+    import paddle.fluid as fluid
+
+    fluid.enable_imperative()  # Now we are in imperative mode
+    x = fluid.layers.ones( (2, 2), "float32")
+    y = fluid.layers.zeros( (2, 2), "float32")
+    z = x + y
+    print( z.numpy() )   #[[1, 1], [1, 1]]
+