refine prelu api doc, test=develop

Author: jerrywgz

python/paddle/fluid/layers/nn.py

@@ -6900,18 +6900,18 @@ def prelu(x, mode, param_attr=None, name=None):
     """
     Equation:
 
-        y = \max(0, x) + alpha \min(0, x)
+        y = \max(0, x) + alpha * \min(0, x)
 
     Args:
         x (Variable): The input tensor.
 	  param_attr(ParamAttr|None): The parameter attribute for the learnable
-                                    weight (alpha).
-        mode (string): The mode for weight sharing
-		       all: all elements share same weight
- 		       channel:elements in a channel share same weight
- 		       element:each element has a weight
+                                      weight (alpha).
+        mode (string): The mode for weight sharing. It supports all, channel
+                       and element. all: all elements share same weight
+                       channel:elements in a channel share same weight
+                       element:each element has a weight
 	name(str|None): A name for this layer(optional). If set None, the layer
-                        will be named automatically.
+                       will be named automatically.
 
     Returns:
         Variable: The output tensor with the same shape as input.
@@ -6921,8 +6921,8 @@ def prelu(x, mode, param_attr=None, name=None):
         .. code-block:: python
 
          x = fluid.layers.data(name="x", shape=[10,10], dtype="float32")
-            mode = 'channel'
-            output = fluid.layers.prelu(x,mode)
+         mode = 'channel'
+         output = fluid.layers.prelu(x,mode)
     """
     helper = LayerHelper('prelu', **locals())
     if mode not in ['all', 'channel', 'element']: