[scripts] Add reduced-context option for TDNN-F layers. (#3658)

Author: danpovey

egs/wsj/s5/steps/libs/nnet3/xconfig/composite_layers.py

@@ -80,7 +80,8 @@ def set_default_configs(self):
                        'time-stride':1,
                        'l2-regularize':0.0,
                        'max-change': 0.75,
-                       'self-repair-scale': 1.0e-05}
+                       'self-repair-scale': 1.0e-05,
+                       'context': 'default'}
 
     def set_derived_configs(self):
         pass
@@ -104,6 +105,10 @@ def check_configs(self):
             raise RuntimeError('bypass-scale is nonzero but output-dim != input-dim: {0} != {1}'
                                ''.format(output_dim, input_dim))
 
+        if not self.config['context'] in ['default', 'left-only', 'shift-left', 'none']:
+            raise RuntimeError('context must be default, left-only shift-left or none, got {}'.format(
+                self.config['context']))
+
 
     def output_name(self, auxiliary_output=None):
         assert auxiliary_output is None
@@ -142,9 +147,16 @@ def _generate_config(self):
         bypass_scale = self.config['bypass-scale']
         dropout_proportion = self.config['dropout-proportion']
         time_stride = self.config['time-stride']
-        if time_stride != 0:
+        context = self.config['context']
+        if time_stride != 0 and context != 'none':
             time_offsets1 = '{0},0'.format(-time_stride)
-            time_offsets2 = '0,{0}'.format(time_stride)
+            if context == 'default':
+                time_offsets2 = '0,{0}'.format(time_stride)
+            elif context == 'shift-left':
+                time_offsets2 = '{0},0'.format(-time_stride)
+            else:
+                assert context == 'left-only'
+                time_offsets2 = '0'
         else:
             time_offsets1 = '0'
             time_offsets2 = '0'