Merge pull request #1010 from goodfeli/fix_clip_grad

theano/scalar/basic.py

@@ -1605,13 +1605,21 @@ class Clip(ScalarOp):
     def c_code(self, node, name, (x, min, max), (z, ), sub):
         return "%(z)s = %(x)s < %(min)s ? %(min)s : %(x)s > %(max)s ? %(max)s : %(x)s;" % locals()
 
-    def grad(self, (x, min, max), (gz, )):
+    def grad(self, (x, mn, mx), (gz, )):
         assert gz.type not in complex_types
-        gx = ((x > min) & (x < max)) * gz
-        if x.type in float_types:
-            return gx, None, None
-        else:
-            return None, None, None
+        gx = ((x > mn) & (x < mx)) * gz
+        gmn = (x < mn) * gz
+        gmx = (x > mx) * gz
+
+        out = self(x, mn, mx)
+
+        def handle_int(v):
+            if out.type in int_types:
+                return v.zeros_like().astype(config.floatX)
+            return v
+
+        return map(handle_int, [gx, gmn, gmx])
+
 # Don't allow complex even if numpy do
 # As there is no mathematical reason for this function on complex
 clip = Clip(upcast_out_no_complex, name='clip')

theano/tensor/tests/test_elemwise.py

@@ -883,6 +883,25 @@ if __name__ == '__main__':
     unittest.TextTestRunner().run(suite)
 """
 
+def test_clip_grad():
+
+    # test the gradient of clip
+    def func(x,y,z):
+        return theano.tensor.clip(x,y,z)
+    # use an x value less than y, an x value between y and z, and an x value
+    # greater than z
+    unittest_tools.verify_grad(func,
+            [ numpy.asarray([-1.,0.5,2.]), 0., 1.])
+
+def test_clip_grad_int():
+
+    # test that integers don't crash clip gradient
+    x = tensor.iscalar()
+    y = tensor.iscalar()
+    z = tensor.iscalar()
+    c = tensor.clip(x,y,z)
+    tensor.grad(c, [x, y, z])
+
 
 if __name__ == '__main__':