.. _program_listing_file_src_rnn_attention.cpp:

Program Listing for File attention.cpp
======================================

|exhale_lsh| :ref:`Return to documentation for file <file_src_rnn_attention.cpp>` (``src/rnn/attention.cpp``)

.. |exhale_lsh| unicode:: U+021B0 .. UPWARDS ARROW WITH TIP LEFTWARDS

.. code-block:: cpp

   #include "attention.h"
   
   #include "graph/node_operators_binary.h"
   #include "tensors/tensor_operators.h"
   
   namespace marian {
   
   namespace rnn {
   
   struct AttentionNodeOp : public NaryNodeOp {
     AttentionNodeOp(const std::vector<Expr>& nodes)
         : NaryNodeOp(nodes, newShape(nodes)) {}
   
     Shape newShape(const std::vector<Expr>& nodes) {
       Shape shape = Shape::broadcast({nodes[1], nodes[2]});
   
       Shape vaShape = nodes[0]->shape();
       ABORT_IF(vaShape[-2] != shape[-1] || vaShape[-1] != 1, "Wrong size");
   
       shape.set(-1, 1);
       return shape;
     }
   
     NodeOps forwardOps() override {
       return {
           NodeOp(Att(val_, child(0)->val(), child(1)->val(), child(2)->val()))};
     }
   
     NodeOps backwardOps() override {
       return {
         NodeOp(AttBack(child(0)->grad(),
                        child(1)->grad(),
                        child(2)->grad(),
                        child(0)->val(),
                        child(1)->val(),
                        child(2)->val(),
                        adj_);)
       };
     }
   
     // do not check if node is trainable
     virtual void runBackward(const NodeOps& ops) override {
       for(auto&& op : ops)
         op();
     }
   
     const std::string type() override { return "Att-ops"; }
   
     const std::string color() override { return "yellow"; }
   };
   
   Expr attOps(Expr va, Expr context, Expr state) {
     std::vector<Expr> nodes{va, context, state};
   
     int dimBatch = context->shape()[-2];
     int dimWords = context->shape()[-3];
     int dimBeam = 1;
     if(state->shape().size() > 3)
       dimBeam = state->shape()[-4];
   
     return reshape(Expression<AttentionNodeOp>(nodes),
                    {dimBeam, 1, dimWords, dimBatch});
   }
   }  // namespace rnn
   }  // namespace marian