Fixup by using the good num_step used and using DisconnectedType instead of…

theano/tensor/basic.py

@@ -5527,7 +5527,7 @@ class ARange(Op):
 
         return [[True], [False], [True]]
 
-    def grad(self, inputs, grads):
+    def L_op(self, inputs, outputs, grads):
         start, stop, step = inputs
         gz, = grads
         # start and step affect the output values
@@ -5541,10 +5541,11 @@ class ARange(Op):
                     DisconnectedType()(),
                     step.zeros_like()]
         else:
-            num_steps_taken = (stop-start)/step
+            num_steps_taken = outputs[0].shape[0]  # (stop-start)/step
             return [gz.sum(dtype=config.floatX),
-                    stop.zeros_like(dtype=config.floatX),
-                    (gz*arange(num_steps_taken+1)).sum(dtype=config.floatX)]
+                    DisconnectedType()(),
+                    (gz * arange(num_steps_taken, dtype=self.dtype)).sum(
+                        dtype=config.floatX)]
 
     def R_op(self, inputs, eval_points):
         return [None]

theano/tensor/tests/test_basic.py

@@ -5912,15 +5912,18 @@ class TestARange(unittest.TestCase):
         assert np.all(f(0, 0, 1) == np.arange(0, 0, 1))
 
     def test_grads(self):
-        start, stop, step = fscalars('start', 'stop', 'step')
         def f(start, stop, step):
             return ARange(start.type.dtype)(start, stop, step)
 
         rng = np.random.RandomState(utt.fetch_seed())
-        utt.verify_grad(f, [np.float32(0),
-                            np.float32(5),
-                            np.float32(1)],
-                        rng=rng)
+        # Due to the random projection, we should not use the exact
+        # point that shage the shape of the output.
+        for start, stop, step in [(0, 4.9, 1),
+                                  (1, 5.1, 0.5)]:
+            utt.verify_grad(f, [np.float32(start),
+                                np.float32(stop),
+                                np.float32(step)],
+                            rng=rng)
 
     def test_integers(self):
         # Test arange constructor, on integer outputs