update per comments

python/mxnet/gluon/loss.py

@@ -306,13 +306,7 @@ class CTCLoss(Loss):
     Sequence Data with Recurrent Neural Networks"
     <http://www.cs.toronto.edu/~graves/icml_2006.pdf>`_ paper for more information.
 
-    The prediction output should be an activation vector without softmax, with shape
-    according to the output_layout:
-    **TNC**: *(sequence_length, batch_size, alphabet_size + 1)*
-    **NTC**: *(batch_size, sequence_length, alphabet_size + 1)*
 
-    The loss output has the shape:
-    **loss**: *(batch_size,)*.
 
     ``label`` is a tensor of integers between 1 and *alphabet_size*, with shape according
     to the label_layout:
@@ -330,69 +324,74 @@ class CTCLoss(Loss):
 
     Parameters
     ----------
-    output_layout : str, default 'NTC'
+    layout : str, default 'NTC'
         Layout of the output sequence activation vector.
     label_layout : str, default 'NT'
         Layout of the labels.
-    use_input_lengths : bool, default False
-        Whether to use `input_lengths` to decide lengths of inputs.
-        If false, the input lengths are treated as being equal to the max sequence length.
-    use_label_lengths : bool, default False
-        Whether to use `label_lengths` to decide lengths of labels.
-        If false, the label lengths are derived from the first occurrence of
-        the value specified by `padding_mask`.
     padding_mask : int or None, default -1
         This is the label value to be considered padding, which is used to derive the actual
-        lengths of labels. Only required when `use_label_lengths` is false.
+        lengths of labels. Only required when `label_lengths` is None.
     weight : float or None
         Global scalar weight for loss.
-    input_lengths : NDArray or None,
-        Actual lengths of inputs. Only required when `use_input_lengths` is true.
-        This should be used as the third argument when calling this loss.
-        The shape should be (N,).
-    label_lengths : NDArray or None,
-        Lengths of labels. Only required when `use_label_lengths` is true.
-        This should be used as the fourth argument when calling this loss.
-        The shape should be (N,).
     sample_weight : Symbol or None
         Per sample weighting. Must be broadcastable to
         the same shape as loss. For example, if loss has
         shape (64, 10) and you want to weight each sample
         in the batch, `sample_weight` should have shape (64, 1).
         This should be used as the fifth argument when calling this loss.
+
+    Input shapes:
+        `data` is an activation tensor without softmax.
+        Its shape depends on `layout`. For `layout='TNC'`, this
+        input has shape `(sequence_length, batch_size, alphabet_size)`
+
+        `label` is the label index matrix.
+        Its shape depends on `layout`. For `layout='TNC'`, this
+        input has shape `(sequence_length, batch_size, alphabet_size)`
+        When `label_lengths` is not specified, the first occurrence of `padding_mask`
+        in each sample marks the end of the label sequence of that sample.
+
+        `data_lengths` is optional and defaults to None.
+        When specified, it represents the actual lengths of data.
+        The shape should be (batch_size,).
+        If None, the data lengths are treated as being equal to the max sequence length.
+        This should be used as the third argument when calling this loss.
+
+        `label_lengths` is optional and defaults to None.
+        When specified, it represents the actual lengths of labels.
+        The shape should be (batch_size,).
+        If None, the label lengths are derived from the first occurrence of
+        the value specified by `padding_mask`.
+        This should be used as the fourth argument when calling this loss.
+
+    Output shape:
+        The CTC loss output has the shape (batch_size,).
     """
-    def __init__(self, output_layout='NTC', label_layout='NT',
-                 use_input_lengths=False, use_label_lengths=False, padding_mask=-1,
+    def __init__(self, layout='NTC', label_layout='NT', padding_mask=-1,
                  weight=None, **kwargs):
-        assert output_layout in ['NTC', 'TNC'],\
-               "Only 'NTC' and 'TNC' layouts for output are supported. Got: %s"%output_layout
+        assert layout in ['NTC', 'TNC'],\
+               "Only 'NTC' and 'TNC' layouts for output are supported. Got: %s"%layout
         assert label_layout in ['NT', 'TN'],\
                "Only 'NT' and 'TN' layouts for label are supported. Got: %s"%label_layout
-        self._output_layout = output_layout
+        self._layout = layout
         self._label_layout = label_layout
-        self._use_input_lengths = use_input_lengths
-        self._use_label_lengths = use_label_lengths
         self._padding_mask = padding_mask
         batch_axis = label_layout.find('N')
         super(CTCLoss, self).__init__(weight, batch_axis, **kwargs)
 
-    def hybrid_forward(self, F, output, label,
+    def hybrid_forward(self, F, data, label,
                        input_lengths=None, label_lengths=None, sample_weight=None):
-        assert not self._use_input_lengths or input_lengths is not None, \
-               "Must specify input_lengths."
-        assert not self._use_label_lengths or label_lengths is not None, \
-               "Must specify label_lengths."
-        if self._output_layout == 'NTC':
-            output = F.swapaxes(output, 0, 1)
+        if self._layout == 'NTC':
+            data = F.swapaxes(data, 0, 1)
         if self._batch_axis == 1:
             label = F.swapaxes(label, 0, 1)
         if F is ndarray:
             F_contrib = ndarray_contrib
         else:
             F_contrib = symbol_contrib
-        loss = F_contrib.CTCLoss(output, label,
-                                 use_input_lengths=self._use_input_lengths,
-                                 use_label_lengths=self._use_label_lengths,
+        loss = F_contrib.CTCLoss(data, label,
+                                 use_input_lengths=input_lengths is not None,
+                                 use_label_lengths=label_lengths is not None,
                                  input_lengths=input_lengths, label_lengths=label_lengths,
                                  padding_mask=self._padding_mask)
         return _apply_weighting(F, loss, self._weight, sample_weight)