Merge pull request #1568 from pascanur/fix_Rop_dot

theano/tensor/basic.py

@@ -4556,11 +4556,12 @@ class Dot(Op):
     def R_op(self, inputs, eval_points):
         # R_op for a \dot b evaluted at c for a and d for b is
         # simply c \dot b + a \dot d
-        if None in eval_points:
-            return [None]
+
 
         assert len(inputs) == 2
         assert len(eval_points) == 2
+        if eval_points[0] is None and eval_points[1] is None:
+            return [None]
 
         debugger_available = config.compute_test_value != 'off'
 
@@ -4579,12 +4580,14 @@ class Dot(Op):
                     'second input passed to Dot.R_op has no test value')
                 debugger_available = False
 
+            if eval_points[0]:
                 try:
                     ev0 = gof.op.get_test_value(eval_points[0])
                 except AttributeError:
                     gof.op.missing_test_message(
                         'first eval point passed to Dot.R_op has no test value')
                     debugger_available = False
+            if eval_points[1]:
                 try:
                     ev1 = gof.op.get_test_value(eval_points[1])
                 except AttributeError:
@@ -4597,7 +4600,8 @@ class Dot(Op):
             eval_point_values = [ev0, ev1]
 
             for i in xrange(2):
-                if input_values[i].shape != eval_point_values[i].shape:
+                if eval_point_values[i] and \
+                   input_values[i].shape != eval_point_values[i].shape:
                     raise ValueError('input ' + str(i) + ' and eval_point ' +
                                      str(i) + ' to Dot.R_op '
                                      'should have the '
@@ -4605,11 +4609,17 @@ class Dot(Op):
                                      ' %s and %s, respectively' % (
                             str(input_values[i].shape),
                             str(eval_point_values[i].shape)))
-
+        if eval_points[0]:
             t1 = self(eval_points[0], inputs[1])
+        if eval_points[1]:
             t2 = self(inputs[0], eval_points[1])
 
+        if eval_points[0] and eval_points[1]:
             return [t1 + t2]
+        elif eval_points[0]:
+            return [t1]
+        else:
+            return [t2]
 
     def infer_shape(self, node, shapes):
         xshp, yshp = shapes

theano/tests/test_rop.py

@@ -347,3 +347,13 @@ class test_RopLop(RopLop_checker):
             all_outs.extend(o)
         f = theano.function([m, v, m_, v_], all_outs)
         f(mval, vval, m_val, v_val)
+
+    def test_Rop_dot_bug_18Oct2013_Jeremiah(self):
+        # This test refers to a bug reported by Jeremiah Lowin on 18th Oct
+        # 2013. The bug consists when through a dot operation there is only
+        # one differentiable path (i.e. there is no gradient wrt to one of
+        # the inputs).
+        x = tensor.arange(20.0).reshape([1, 20])
+        v = theano.shared(numpy.ones([20]))
+        d = tensor.dot(x, v).sum()
+        tensor.Rop(tensor.grad(d, v), v, v)