add mish cn docs (PaddlePaddle#4186)

* add mish cn docs

* modify example of mish in static graph

* modify docs of mish

docs/api/api_label

@@ -586,6 +586,7 @@ paddle.fluid.layers.nn.mul	.. _api_paddle_fluid_layers_nn_mul:
 paddle.fluid.layers.learning_rate_scheduler.exponential_decay	.. _api_paddle_fluid_layers_learning_rate_scheduler_exponential_decay:
 paddle.static.nn.sequence_slice	.. _api_paddle_static_nn_sequence_slice:
 paddle.fluid.layers.nn.swish	.. _api_paddle_fluid_layers_nn_swish:
+paddle.fluid.layers.nn.mish	.. _api_paddle_fluid_layers_nn_mish:
 paddle.fluid.layers.nn.chunk_eval	.. _api_paddle_fluid_layers_nn_chunk_eval:
 paddle.fluid.layers.nn.reshape	.. _api_paddle_fluid_layers_nn_reshape:
 paddle.fluid.layers.nn.brelu	.. _api_paddle_fluid_layers_nn_brelu:
@@ -870,6 +871,7 @@ paddle.nn.GroupNorm	.. _api_paddle_nn_GroupNorm:
 paddle.nn.Pad2D	.. _api_paddle_nn_Pad2D:
 paddle.nn.ELU	.. _api_paddle_nn_ELU:
 paddle.nn.Swish	.. _api_paddle_nn_Swish:
+paddle.nn.Mish	.. _api_paddle_nn_Mish:
 paddle.nn.RNN	.. _api_paddle_nn_RNN:
 paddle.nn.Softsign	.. _api_paddle_nn_Softsign:
 paddle.nn.Tanh	.. _api_paddle_nn_Tanh:
@@ -916,6 +918,7 @@ paddle.nn.functional.cosine_similarity	.. _api_paddle_nn_functional_cosine_simil
 paddle.nn.functional.log_softmax	.. _api_paddle_nn_functional_log_softmax:
 paddle.nn.functional.binary_cross_entropy	.. _api_paddle_nn_functional_binary_cross_entropy:
 paddle.nn.functional.swish	.. _api_paddle_nn_functional_swish:
+paddle.nn.functional.mish	.. _api_paddle_nn_functional_mish:
 paddle.nn.functional.conv2d_transpose	.. _api_paddle_nn_functional_conv2d_transpose:
 paddle.nn.functional.tanhshrink	.. _api_paddle_nn_functional_tanhshrink:
 paddle.nn.functional.softplus	.. _api_paddle_nn_functional_softplus:

docs/api/paddle/fluid/layers/mish_cn.rst

@@ -0,0 +1,47 @@
+.. _cn_api_fluid_layers_mish:
+
+mish
+-------------------------------
+
+.. py:function:: paddle.fluid.layers.mish(x, threshold=20, name=None)
+
+
+
+
+Mish激活函数。参考 `Mish: A Self Regularized Non-Monotonic Neural Activation Function <https://arxiv.org/abs/1908.08681>`_ 。
+
+.. math::
+        softplus(x) = \begin{cases}
+                x, \text{if } x > \text{threshold} \\
+                \ln(1 + e^{x}),  \text{otherwise}
+            \end{cases}
+
+        Mish(x) = x * \tanh(softplus(x))
+
+参数：
+    - **x** (Variable) -  多维 Tensor 或 LoDTensor，数据类型为 float32，float64。
+    - **threshold** (float) - Mish激活函数中计算softplus的阈值。如果输入大于该阈值，将使用近似计算，默认值为 20.0。
+    - **name** (str，可选) – 具体用法请参见 :ref:`api_guide_Name` ，一般无需设置，默认值为None。
+
+返回：
+    - Variable: Mish op 的结果，多维 Tensor 或 LoDTensor。数据类型为 float32 或 float64，数据类型以及形状和输入 x 一致。
+
+**代码示例：**
+
+.. code-block:: python
+
+    import paddle
+    paddle.enable_static()
+    import paddle.fluid as fluid
+    import numpy as np
+    DATATYPE='float32'
+    x_data = np.array([i for i in range(1,5)]).reshape([1,1,4]).astype(DATATYPE)
+    x = fluid.data(name="x", shape=[None,1,4], dtype=DATATYPE)
+    y = fluid.layers.mish(x)
+    place = fluid.CPUPlace()
+    # place = fluid.CUDAPlace(0)
+    exe = fluid.Executor(place)
+    out, = exe.run(feed={'x':x_data}, fetch_list=[y.name])
+    print(out)  # [[0.66666667, 1.66666667, 3., 4.]]
+
+

docs/api/paddle/nn/Mish_cn.rst

@@ -0,0 +1,37 @@
+.. _cn_api_nn_Mish:
+
+Mish
+-------------------------------
+.. py:class:: paddle.nn.Mish(name=None)
+
+Mish激活层
+
+.. math::
+
+        softplus(x) = \begin{cases}
+                x, \text{if } x > \text{threshold} \\
+                \ln(1 + e^{x}),  \text{otherwise}
+            \end{cases}
+
+        Mish(x) = x * \tanh(softplus(x))
+
+
+参数
+::::::::::
+    - name (str, 可选) - 操作的名称(可选，默认值为None）。更多信息请参见 :ref:`api_guide_Name`。
+
+形状:
+::::::::::
+    - input: 任意形状的Tensor。
+    - output: 和input具有相同形状的Tensor。
+
+代码示例
+:::::::::
+
+.. code-block:: python
+
+    import paddle
+
+    x = paddle.to_tensor([-5., 0., 5.])
+    m = paddle.nn.Mish()
+    out = m(x) # [-0.03357624, 0., 4.99955208]

docs/api/paddle/nn/Overview_cn.rst

@@ -135,6 +135,7 @@ Padding层
     " :ref:`paddle.nn.Softshrink <cn_api_nn_Softshrink>` ", "Softshrink激活层"
     " :ref:`paddle.nn.Softsign <cn_api_nn_Softsign>` ", "Softsign激活层"
     " :ref:`paddle.nn.Swish <cn_api_nn_Swish>` ", "Swish激活层"
+    " :ref:`paddle.nn.Mish <cn_api_nn_Mish>` ", "Mish激活层"
     " :ref:`paddle.nn.Tanh <cn_api_nn_Tanh>` ", "Tanh激活层"
     " :ref:`paddle.nn.Tanhshrink <cn_api_nn_Tanhshrink>` ", "Tanhshrink激活层"
     " :ref:`paddle.nn.ThresholdedReLU <cn_api_nn_ThresholdedReLU>` ", "Thresholded ReLU激活层"
@@ -382,6 +383,7 @@ Padding相关函数
     " :ref:`paddle.nn.functional.softshrink <cn_api_nn_cn_softshrink>` ", "softshrink激活函数"
     " :ref:`paddle.nn.functional.softsign <cn_api_nn_cn_softsign>` ", "softsign激活函数"
     " :ref:`paddle.nn.functional.swish <cn_api_nn_cn_swish>` ", "swish激活函数"
+    " :ref:`paddle.nn.functional.mish <cn_api_nn_cn_mish>` ", "mish激活函数"
     " :ref:`paddle.nn.functional.tanhshrink <cn_api_nn_cn_tanhshrink>` ", "tanhshrink激活函数"
     " :ref:`paddle.nn.functional.thresholded_relu <cn_api_nn_cn_thresholded_relu>` ", "thresholded_relu激活函数"
 

docs/api/paddle/nn/functional/mish_cn.rst

@@ -0,0 +1,38 @@
+.. _cn_api_nn_cn_mish:
+
+mish
+-------------------------------
+
+.. py:function:: paddle.nn.functional.mish(x, name=None)
+
+mish激活层。计算公式如下：
+
+.. math::
+
+        softplus(x) = \begin{cases}
+                x, \text{if } x > \text{threshold} \\
+                \ln(1 + e^{x}),  \text{otherwise}
+            \end{cases}
+
+        Mish(x) = x * \tanh(softplus(x))
+
+
+参数
+::::::::::
+    - x (Tensor) - 输入的 ``Tensor`` ，数据类型为：float32、float64。
+    - name (str, 可选) - 操作的名称(可选，默认值为None）。更多信息请参见 :ref:`api_guide_Name`。
+
+返回
+::::::::::
+    ``Tensor`` ，数据类型和形状同 ``x`` 一致。
+
+代码示例
+::::::::::
+
+.. code-block:: python
+
+    import paddle
+    import paddle.nn.functional as F
+
+    x = paddle.to_tensor([-5., 0., 5.])
+    out = F.mish(x) # [-0.03357624, 0., 4.99955208]