instead of a connection matrix

theano/scan_module/scan_op.py

@@ -1291,6 +1291,7 @@ class Scan(PureOp):
                      if x in diff_inputs])
             return [gmp.get(p, None) for p in diff_inputs]
         dC_dinps_t = [None for inp in diff_inputs]
+        disconnected_dC_dinps_t = [True for inp in diff_inputs]
         dC_dXts = []
         Xts = []
         for idx, Xt in enumerate(diff_outputs):
@@ -1325,13 +1326,11 @@ class Scan(PureOp):
                 elif _dC_dinps_t[jdx]:
                     dC_dinps_t[jdx] += _dC_dinps_t[jdx]
         # mask inputs that get no gradients
-        disconnected_dC_dinps_t = []
         for dx in xrange(len(dC_dinps_t)):
             if not dC_dinps_t[dx]:
                 dC_dinps_t[dx] = tensor.zeros_like(diff_inputs[dx])
-                disconnected_dC_dinps_t.append(True)
             else:
-                disconnected_dC_dinps_t.append(False)
+                disconnected_dC_dinps_t[dx] = False
                 for Xt, Xt_placeholder in zip(
                         diff_outputs[self.n_mit_mot_outs:],
                         Xts):