Fix EighGrad that didn't returned the good dtype when the input is float32.

theano/sandbox/linalg/ops.py

@@ -1033,7 +1033,18 @@ class EighGrad(Op):
 
     def make_node(self, x, w, v, gw, gv):
         x, w, v, gw, gv = map(as_tensor_variable, (x, w, v, gw, gv))
-        return Apply(self, [x, w, v, gw, gv], [x.type()])
+        assert x.ndim == 2
+        assert w.ndim == 1
+        assert v.ndim == 2
+        assert gw.ndim == 1
+        assert gv.ndim == 2
+        if x.dtype == "float32":
+            # The call to self.tri0 in perform upcast from float32 to
+            # float64.
+            out = theano.tensor.matrix(dtype="float64")
+        else:
+            out = x.type()
+        return Apply(self, [x, w, v, gw, gv], [out])
 
     def perform(self, node, inputs, outputs):
         r"""