autograd.cpp.diff

diff --git a/autograd.cpp b/autograd.cpp
index aa849d6..5c3896b 100644
--- a/autograd.cpp
+++ b/autograd.cpp
@@ -9,7 +9,7 @@ tag::Engine engine;
 void backward(Variable loss, bool keep_graph) {
   tag::function_list funclst;
   funclst.emplace_back(loss.grad_fn(), loss.output_nr());
-  detail::engine.execute(funclst, {Var(at::ones_like(loss.data()))}, false);
+  detail::engine.execute(funclst, {Var(at::ones_like(loss.data()), false, true)}, false);
 }
 
 std::unordered_map<std::string, Variable> ContainerImpl::parameters() {