Update comments for two operators. (#7457)

* update code comments.

* update the comments.

* follow comments.

paddle/operators/reorder_lod_tensor_by_rank_op.cc

@@ -26,22 +26,44 @@ class ReorderLoDTensorByRankTableOpProtoMaker
   ReorderLoDTensorByRankTableOpProtoMaker(OpProto *proto,
                                           OpAttrChecker *op_checker)
       : OpProtoAndCheckerMaker(proto, op_checker) {
-    AddInput("X", "(LoDTensor) the input lod tensor need to be reordered.");
+    AddInput("X",
+             "(LoDTensor), the input lod tensor to be reordered according to "
+             "Input(RankTable).");
     AddInput("RankTable",
-             "(LoDRankTable) the rank table that input need follow");
-    AddOutput("Out", "(LoDTensor) reordered lod tensor");
-    AddComment(R"DOC(ReorderLoDTensorByRankTable
+             "(LoDRankTable), the rank table according to which Input(X) is "
+             "reordered.");
+    AddOutput("Out", "(LoDTensor), the reordered lod tensor.");
+    AddComment(R"DOC(ReorderLoDTensorByRankTable operator.
 
-Reorder the input X by the rank of `RankTable`. If `RankTable` is ordered by
-index [3, 0, 2, 1]. Input X will reorder its sequence, the third sequence of
-X will be the first sequence of Output.
-
-NOTE: The RankTable does not need to be calculated by X.
+Input(X) is a batch of sequences. Input(RankTable) stores new orders of the
+input sequence batch. The reorder_lod_tensor_by_rank operator reorders the
+Input(X) according to the information provided by Input(RankTable).
 
 For example:
-The X = [Seq0, Seq1, Seq2, Seq3]. The indices of RankTable are [3, 0, 2, 1].
 
-The Out =  [Seq3, Seq0, Seq2, Seq1] with correct LoD information.
+If the indices stored in the Input(RankTable) are [3, 0, 2, 1], the
+Input(X) will be reordered that the fourth sequence in Input(X) will become the
+first one, and then followed by the original first, third, and the second one.
+
+This is:
+X = [Seq0, Seq1, Seq2, Seq3]. The indices in RankTable are [3, 0, 2, 1].
+Out =  [Seq3, Seq0, Seq2, Seq1] with a new LoD information.
+
+If the LoD information of Input(X) is empty, this means Input(X) is not sequence
+data. This is also identical to a batch of sequences where each sequence has a
+fixed length 1. In this case, the reorder_lod_tensor_by_rank operator reorders
+each slice of Input(X) along the first axis according to Input(RankTable).
+
+This is:
+X = [Slice0, Slice1, Slice2, Slice3] and its LoD information is empty. The
+indices in RankTable are [3, 0, 2, 1].
+Out = [Slice3, Slice0, Slice2, Slice1] with no LoD information is appended.
+
+NOTE: This operator sorts Input(X) according to a given LoDRankTable which does
+not need to be calculated according to Input(X). It can be calculated according
+to another different sequence, and then this operator sorts Input(X) according
+to the given LoDRankTable.
+
 )DOC");
   }
 };

paddle/operators/shrink_rnn_memory_op.cc

@@ -45,7 +45,7 @@ class ShrinkRNNMemoryOp : public ArrayOp {
         rank_items.begin();
 
     auto *out_var = scope.FindVar(Output("Out"));
-    PADDLE_ENFORCE(out_var != nullptr, "Output Out must be set");
+    PADDLE_ENFORCE(out_var != nullptr, "Output(Out) must be set.");
     auto &out_tensor = *out_var->GetMutable<framework::LoDTensor>();
 
     size_t height = dst_num_rows;
@@ -76,15 +76,17 @@ class ShrinkRNNMemoryOpProtoMaker : public framework::OpProtoAndCheckerMaker {
              "(LoDTensor) The step index. The RNN step memory 'X' will be "
              "shrinked to match the size of the input of the index'th step.");
     AddOutput("Out", "(LoDTensor) The shrinked RNN step memory.");
-    AddComment(
-        R"DOC(
-        In dynamic RNN, we are able to handle sequences of different lengths.
-        Because of the multiple lengths, the size of each step input can be
-        different, which may lead to a mismatching between the input of
-        the current step and the memory generated by the previous one. This
-        operator shrinks memory according to the size of the next step input,
-        to make sure that they can match each other.
-        )DOC");
+    AddComment(R"DOC(
+This operator is used to shrink output batch of memory defined in dynamic RNN.
+
+Dynamic RNN is able to handle variable-length sequences, in which, sequences in
+a mini-batch are sorted by their lengths first. After that, the longest sequence
+becomes the first one in the sorted batch, followed by the second longest, the
+third longest, and so on. Dynamic RNN then slices a batch input timestep by
+timestep from the sorted input. Once any sequence in the input batch reaches its
+end, memory defined in dynamicRNN has to shrink its outputs to adapt to the input
+batch size for the next time step.
+)DOC");
   }
 };
 

python/paddle/v2/fluid/layers/control_flow.py

@@ -742,11 +742,10 @@ def topk(input, k):
 
 
 def lod_tensor_to_array(x, table):
-    """This function performs the operation that converts an LOD_Tensor to
-       an array.
+    """ Convert a LOD_TENSOR to an LOD_TENSOR_ARRAY.
 
     Args:
-        x (Variable|list): The tensor that needs to be converted to an array.
+        x (Variable|list): The LOD tensor to be converted to a LOD tensor array.
         table (ParamAttr|list): The variable that stores the level of lod
                                 which is ordered by sequence length in
                                 descending order.
@@ -776,11 +775,10 @@ def lod_tensor_to_array(x, table):
 
 
 def array_to_lod_tensor(x, table):
-    """This function performs the operations that converts an array to
-       an LOD_Tensor.
+    """Convert a LoD_Tensor_Aarry to an LoDTensor.
 
     Args:
-        x (Variable|list): The array that needs to be converted to a tensor.
+        x (Variable|list): The lod tensor array to be converted to a tensor.
         table (ParamAttr|list): The variable that stores the level of lod
                                 which is ordered by sequence length in
                                 descending order.
@@ -808,7 +806,8 @@ def array_to_lod_tensor(x, table):
 
 
 def increment(x, value=1.0, in_place=True):
-    """This function performs an operation that increments each value in the
+    """
+    This function performs an operation that increments each value in the
     input :math:`x` by an amount: :math:`value` as mentioned in the input
     parameter. This operation is performed in-place by default.
 
@@ -841,17 +840,24 @@ def increment(x, value=1.0, in_place=True):
 
 
 def array_write(x, i, array=None):
-    """This function performs the operation to write the data out as an
-    LOD_TENSOR_ARRAY.
+    """
+    This function writes the given input variable to the specified position
+    indicating by the arrary index to an output LOD_TENSOR_ARRAY. If the
+    output LOD_TENSOR_ARRAY is not given(None), a new one will be created and
+    returned.
 
     Args:
         x (Variable|list): The input tensor from which the data will be read.
-        i (Variable|list): The subscript index in tensor array, that points the
-                           place from which data will be read.
-        array (Variable|list): The data can be read into this variable if
-                               this is assigned.
+        i (Variable|list): The index of the output LOD_TENSOR_ARRAY, pointing to
+                           the position to which the input tensor will be
+                           written.
+        array (Variable|list): The output LOD_TENSOR_ARRAY to which the input
+                               tensor will be written. If this parameter is
+                               NONE, a new LOD_TENSOR_ARRAY will be created and
+                               returned.
+
     Returns:
-        Variable: The tensor type variable that has the data written to it.
+        Variable: The output LOD_TENSOR_ARRAY where the input tensor is written.
 
     Examples:
         .. code-block::python
@@ -1228,7 +1234,7 @@ class DynamicRNN(object):
         self._assert_in_rnn_block_("step_input")
         if not isinstance(x, Variable):
             raise TypeError(
-                "step_input() can only take a Variable as its input")
+                "step_input() can only take a Variable as its input.")
         parent_block = self._parent_block_()
         if self.lod_rank_table is None:
             self.lod_rank_table = parent_block.create_var(
@@ -1289,8 +1295,8 @@ class DynamicRNN(object):
 
     def __call__(self, *args, **kwargs):
         if self.status != DynamicRNN.AFTER_RNN:
-            raise ValueError(
-                "Dynamic RNN outputs can only be retrieved after rnn block")
+            raise ValueError(("Output of the dynamic RNN can only be visited "
+                              "outside the rnn block."))
         if len(self.outputs) == 1:
             return self.outputs[0]
         else:

python/paddle/v2/fluid/layers/tensor.py

@@ -176,25 +176,26 @@ def fill_constant(shape, dtype, value, out=None):
     """
     **fill_constant**
 
-    This function creates a tensor of specified *shape* and
-    *dtype*, and initializes this with a constant supplied in *value*.
+    This function creates a tensor with specified `shape` and `dtype`, and
+    initializes it with a constant specifed by `value`.
 
-    It also sets *stop_gradient* to True.
+    The attribute `stop_gradient` of the created tensor is set to True.
 
     Args:
-        shape(tuple|list|None): Shape of output tensor
-        dtype(np.dtype|core.DataType|str): Data type of output tensor
-        value(float): Constant value to initialize the output tensor
-        out(Variable): Output Variable to initialize
+        shape(tuple|list|None): Shape of the output tensor.
+        dtype(np.dtype|core.DataType|str): Data type of the output tensor.
+        value(float): The constant value used to initialize the output tensor.
+        out(Variable): The output tensor.
 
     Returns:
-        Variable: The tensor variable storing the output
+        Variable: The tensor variable storing the output.
 
     Examples:
         .. code-block:: python
 
           data = fluid.layers.fill_constant(shape=[1], value=0, dtype='int64')
     """
+
     helper = LayerHelper("fill_constant", **locals())
     if out is None:
         out = helper.create_tmp_variable(dtype=dtype)