Created setGrad() function.

src/chainable.h

@@ -49,10 +49,13 @@ struct Chainable {
     
     virtual const Shape& shape() = 0;
     virtual const DataType &val() = 0;
-    virtual DataType grad() = 0;
+    virtual const DataType &grad() = 0;
     virtual void setVal(DataType t) {
       UTIL_THROW2("Tensors can only be assigned to input and parameter nodes"); 
     };
+    virtual void setGrad(DataType t) {
+      UTIL_THROW2("Gradients can only be assigned to parameter nodes"); 
+    };
 };
 
 // XXX Marcin, is ChainableStack the most appropriate name?

src/expression_graph.cu

@@ -29,7 +29,7 @@ Expr::Expr(ExpressionGraphPtr g, Chainable<Tensor>* chainable)
   graph_->stack()->push_back(chainable);    
 }
 
-Tensor Expr::val() {
+const Tensor &Expr::val() {
   return pimpl_->val();
 }
 
@@ -37,8 +37,12 @@ void Expr::setVal(const Tensor &val) {
   pimpl_->setVal(val);
 }
 
-Tensor Expr::grad() {
-    return pimpl_->grad();
+const Tensor &Expr::grad() {
+  return pimpl_->grad();
+}
+
+void Expr::setGrad(const Tensor &grad) {
+  pimpl_->setGrad(grad);
 }
 
 ChainPtr Expr::node() {

src/expression_graph.h

@@ -45,10 +45,11 @@ class Expr {
       return *this;
     }
 
-    Tensor val();
-    Tensor grad();
+    const Tensor &val();
+    const Tensor &grad();
 
     void setVal(const Tensor &val);
+    void setGrad(const Tensor &grad);
 
     ExpressionGraphPtr graph();
     

src/node.h

@@ -80,7 +80,7 @@ class Node : public Chainable<Tensor>,
       return val_;
     };
     
-    virtual Tensor grad() {
+    virtual const Tensor &grad() {
       UTIL_THROW_IF2(!adj_, "Tensor has not been allocated");
       return adj_;
     };

src/node_operators.h

@@ -92,6 +92,12 @@ struct ParamNode : public Node {
     //@todo, shape checking
   };
 
+  virtual void setGrad(Tensor t)  {
+    adj_ = t;
+    shape_ = t.shape();
+    //@todo, shape checking
+  };
+
   void forward() {}
   void backward() {}
   

src/validate_encoder_decoder.cu

@@ -224,9 +224,11 @@ int main(int argc, char** argv) {
       //ExpressionGraph g = graphs[b];
       ExpressionGraph g = graphs[b0];
       // Share the parameters.
+      std::cerr << j << std::endl;
       if (false && b != b0) {
         for (int i = 0; i < g.params().size(); ++i) {
           g.params()[i].setVal(graphs[b0].params()[i].val());
+          g.params()[i].setGrad(graphs[b0].params()[i].grad());
         }
       }