Fixed bug related to gradients trough a cast.

I have changed the gradients trough a cast to be defined if and only if both the input and output are of continuous types.

Fixed bug related to gradients trough a cast.
95bcd449 · Razvan Pascanu · d47333ed · 95bcd449
--- a/theano/scalar/basic.py
+++ b/theano/scalar/basic.py
@@ -1290,7 +1290,7 @@ class Cast(UnaryScalarOp):
    def c_code(self, node, name, (x, ), (z, ), sub):
        return "%s = (%s)%s;" % (z, node.outputs[0].type.dtype_specs()[1], x)
    def grad(self, (x, ), (gz, )):
-        if x.type in continuous_types:
+        if x.type in continuous_types and self.o_type in continuous_types:
            return [cast(gz, x.type.dtype)]
        else:
            return None,