check first if disconnected, afterwards if undefined

theano/scan_module/scan_op.py

@@ -1690,36 +1690,46 @@ class Scan(PureOp):
         for p, (x, t) in enumerate(
             zip(outputs[offset:offset + self.n_seqs],
                 type_outs[offset:offset + self.n_seqs])):
-            if t == 'undefined':
-
+            if t == 'disconnected':
+                gradients.append(DisconnectedType()())
+            elif t == 'undefined':
                 gradients.append(
                     grad_undefined(self,
                                    p + 1,
                                    inputs[p + 1],
                                    'Depends on a shared variable'))
-            elif t == 'disconnected':
-                gradients.append(DisconnectedType()())
             else:
                 gradients.append(x[::-1])
         end = self.n_mit_mot + self.n_mit_sot + self.n_sit_sot
         for p, (x, t) in enumerate(
             zip(outputs[:end], type_outs[:end])):
-            if t == 'undefined':
+            if t == 'disconnected':
+                gradients.append(DisconnectedType()())
+            elif t == 'undefined':
                 gradients.append(
                     grad_undefined(self,
                                    p + 1 + self.n_seqs,
                                    inputs[p + 1 + self.n_seqs],
                                    'Depends on a shared variable'))
-            elif t == 'disconnected':
-                gradients.append(DisconnectedType()())
             else:
                 gradients.append(x[::-1])
 
         start = len(gradients)
-        gradients += [
-                grad_undefined(self, x + start, inputs[x + start],
-                    'Shared Variable with update')
-                for x in xrange(self.n_shared_outs)]
+        node = outs[0].owner
+        for idx in xrange(self.n_shared_outs):
+            disconnected = True
+            connected_flags = self.connection_pattern(node)[idx+start]
+            for dC_dout, connected in zip(dC_douts, connected_flags):
+                if (not isinstance(dC_dout.type, DisconnectedType) and
+                        connected):
+                    disconnected = False
+            if disconnected:
+                gradients.append(DisconnectedType()())
+            else:
+                gradients.append(grad_undefined(
+                    self, idx, inputs[idx],
+                    'Shared Variable with update'))
+
         start = len(gradients)
         gradients += [DisconnectedType()()
                 for x in xrange(self.n_nit_sot)]
@@ -1728,14 +1738,14 @@ class Scan(PureOp):
         end = begin + n_sitsot_outs
         for p, (x, t) in enumerate(
             zip(outputs[begin:end], type_outs[begin:end])):
-            if t == 'undefined':
+            if t == 'disconnected':
+                gradients.append(DisconnectedType()())
+            elif t == 'undefined':
                 gradients.append(
                     grad_undefined(self,
                                    p + begin + 1,
                                    inputs[p + begin + 1],
                                    'Depends on a shared variable'))
-            elif t == 'disconnected':
-                gradients.append(DisconnectedType()())
             else:
                 gradients.append(x[-1])
         return gradients