R_op for ZeroGrad + tests

theano/gradient.py

@@ -1973,6 +1973,11 @@ class ZeroGrad(ViewOp):
     def grad(self, args, g_outs):
         return [g_out.zeros_like(g_out) for g_out in g_outs]
 
+    def R_op(self, inputs, eval_points):
+        if eval_points[0] is None:
+            return [None]
+        
+        return theano.tensor.zeros(1)
 
 zero_grad_ = ZeroGrad()
 

theano/tests/test_gradient.py

@@ -663,7 +663,7 @@ class TestZeroGrad(unittest.TestCase):
         x = theano.tensor.matrix('x')
         y = x * gradient.zero_grad(x)
         f = theano.function([x], y)
-        # need to refer to theano.gradient.zero_grad here,
+        # need to refer to theano.ogradient.zero_grad here,
         # theano.gradient.zero_grad is a wrapper function!
         assert gradient.zero_grad_ not in \
             [node.op for node in f.maker.fgraph.toposort()]
@@ -691,6 +691,23 @@ class TestZeroGrad(unittest.TestCase):
 
             assert np.allclose(f(a), f2(a))
 
+    def test_rop(self):
+        T = theano.tensor
+
+        x = T.vector()
+        v = T.vector() 
+        y = gradient.zero_grad(x)
+
+        rop = T.Rop(y, x, v)
+        f = theano.function([x, v], rop, on_unused_input='ignore')
+
+        a = np.asarray(self.rng.randn(5),
+                        dtype=config.floatX)
+        u = np.asarray(self.rng.randn(5),
+                        dtype=config.floatX)
+
+        assert np.count_nonzero(f(a,u)) == 0
+
 
 class TestDisconnectedGrad(unittest.TestCase):