Polish doc

test=develop

python/paddle/fluid/layers/nn.py

@@ -5830,25 +5830,31 @@ def rank_loss(label, left, right, name=None):
 
 def margin_rank_loss(label, left, right, margin=0.1, name=None):
     """
-    **Margin Rank loss layer for rank problem**
-     Args:
-        label (Variable): Indicats whether left higher than (right + margin) or not.
-        left (Variable): rank score for left.
-        right (Variable): rank score for right.
-        margin (float): Indicates the margin to be added to right
-        name (str|None): A name for this layer (optional). If set None, the layer
-                        will be named automatically.
-     Returns:
-        list: The value of rank loss.
-     Raises:
-        ValueError: Any of label, left, and right is not a variable.
-     Examples:
-         .. code-block:: python
-            label = fluid.layers.data(name="label", shape=[4, 1], dtype="float32")
-            left = fluid.layers.data(name="left", shape=[4, 1], dtype="float32")
-            right = fluid.layers.data(name="right", shape=[4, 1], dtype="float32")
-            out = fluid.layers.margin_rank_loss(label, left, right)
-     """
+    Margin Rank loss layer for rank problem, which comparing left value and right value be passed in.
+    The rank loss can be defined as below equation:
+
+    .. math::
+
+        rank\_loss &= max(0, -label * (left - right) + margin)
+
+    Args:
+       label (Variable): Indicats whether left higher than (right + margin) or not.
+       left (Variable): rank score for left.
+       right (Variable): rank score for right.
+       margin (float): Indicates the margin to be added to right
+       name (str|None): A name for this layer (optional). If set None, the layer
+                       will be named automatically.
+    Returns:
+       list: The value of rank loss.
+    Raises:
+       ValueError: Any of label, left, and right is not a variable.
+    Examples:
+        .. code-block:: python
+           label = fluid.layers.data(name="label", shape=[4, 1], dtype="float32")
+           left = fluid.layers.data(name="left", shape=[4, 1], dtype="float32")
+           right = fluid.layers.data(name="right", shape=[4, 1], dtype="float32")
+           out = fluid.layers.margin_rank_loss(label, left, right)
+    """
     helper = LayerHelper('margin_rank_loss', **locals())
     if not (isinstance(label, Variable)):
         raise ValueError("The label should be a Variable")