gru.h

#ifndef DYNET_GRU_H_
#define DYNET_GRU_H_

#include "dynet/dynet.h"
#include "dynet/rnn.h"

namespace dynet {

class ParameterCollection;

struct GRUBuilder : public RNNBuilder {
  GRUBuilder() = default;
  explicit GRUBuilder(unsigned layers,
                      unsigned input_dim,
                      unsigned hidden_dim,
                      ParameterCollection& model);
  Expression back() const override { return (cur == -1? h0.back() : h[cur].back()); }
  std::vector<Expression> final_h() const override { return (h.size() == 0 ? h0 : h.back()); }
  std::vector<Expression> final_s() const override { return final_h(); }
  std::vector<Expression> get_h(RNNPointer i) const override { return (i == -1 ? h0 : h[i]); }
  std::vector<Expression> get_s(RNNPointer i) const override { return get_h(i); }
  unsigned num_h0_components() const override { return layers; }
  void copy(const RNNBuilder & params) override;
  ParameterCollection & get_parameter_collection() override;


  // first index is layer, then ...
  std::vector<std::vector<Parameter>> params;
  // first index is layer, then ...
  std::vector<std::vector<Expression>> param_vars;

 protected:
  void new_graph_impl(ComputationGraph& cg, bool update) override;
  void start_new_sequence_impl(const std::vector<Expression>& h0) override;
  Expression add_input_impl(int prev, const Expression& x) override;
  Expression set_h_impl(int prev, const std::vector<Expression>& h_new) override;
  Expression set_s_impl(int prev, const std::vector<Expression>& s_new) override;

  ParameterCollection local_model;

  // first index is time, second is layer
  std::vector<std::vector<Expression>> h;

  // initial values of h at each layer
  // - default to zero matrix input
  std::vector<Expression> h0;

  unsigned hidden_dim;
  unsigned layers;
};

} // namespace dynet

#endif