classical_ising.hpp

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//    Copyright 2023 Jij Inc.
 
//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at
 
//        http://www.apache.org/licenses/LICENSE-2.0
 
//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.
 
#pragma once
 
#include <cassert>
#include <type_traits>
#include <utility>
 
#include <Eigen/Dense>
#include <Eigen/Sparse>
 
#include <cimod/utilities.hpp>
 
#include "openjij/graph/all.hpp"
#include "openjij/system/system.hpp"
#include "openjij/utility/eigen.hpp"
 
namespace openjij {
namespace system {
 
template <typename GraphType> struct ClassicalIsing;
 
template <typename FloatType> struct ClassicalIsing<graph::Dense<FloatType>> {
  using system_type = classical_system;
 
  // matrix (row major)
  using MatrixXx =
      Eigen::Matrix<FloatType, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>;
  // vector (col major)
  using VectorXx = Eigen::Matrix<FloatType, Eigen::Dynamic, 1, Eigen::ColMajor>;
 
  ClassicalIsing(const graph::Spins &init_spin,
                 const graph::Dense<FloatType> &init_interaction)
      : spin(utility::gen_vector_from_std_vector<FloatType, Eigen::ColMajor>(
            init_spin)),
        interaction(init_interaction.get_interactions()),
        num_spins(init_interaction.get_num_spins()) {
    cimod::CheckVariables(init_spin, cimod::Vartype::SPIN);
    assert(init_spin.size() == init_interaction.get_num_spins());
    reset_dE();
  }
 
  void reset_spins(const graph::Spins &init_spin) {
    this->spin =
        utility::gen_vector_from_std_vector<FloatType, Eigen::ColMajor>(
            init_spin);
    reset_dE();
  }
 
  inline void reset_dE() {
    this->dE =
        -2.0 * this->spin.array() * (this->interaction * this->spin).array();
  }
 
  VectorXx spin;
 
  const MatrixXx interaction;
 
  const std::size_t num_spins; // spin.size()-1
 
  VectorXx dE;
};
 
template <typename FloatType> struct ClassicalIsing<graph::Sparse<FloatType>> {
  using system_type = classical_system;
 
  // matrix (row major)
  using SparseMatrixXx = Eigen::SparseMatrix<FloatType, Eigen::RowMajor>;
  // vector (col major)
  using VectorXx = Eigen::Matrix<FloatType, Eigen::Dynamic, 1, Eigen::ColMajor>;
 
  ClassicalIsing(const graph::Spins &init_spin,
                 const graph::Sparse<FloatType> &init_interaction)
      : spin(utility::gen_vector_from_std_vector<FloatType, Eigen::ColMajor>(
            init_spin)),
        interaction(
            utility::gen_matrix_from_graph<Eigen::RowMajor>(init_interaction)),
        num_spins(init_interaction.get_num_spins()) {
    assert(init_spin.size() == init_interaction.get_num_spins());
    reset_dE();
  }
 
  void reset_spins(const graph::Spins &init_spin) {
    this->spin =
        utility::gen_vector_from_std_vector<FloatType, Eigen::ColMajor>(
            init_spin);
    reset_dE();
  }
 
  void reset_dE() {
    this->dE =
        -2.0 * this->spin.array() * (this->interaction * this->spin).array();
  }
 
  VectorXx spin;
 
  const SparseMatrixXx interaction;
 
  const std::size_t num_spins; // spin.size()-1
 
  VectorXx dE;
};
 
template <typename FloatType> struct ClassicalIsing<graph::CSRSparse<FloatType>> {
  using system_type = classical_system;
 
  // matrix (row major)
  using SparseMatrixXx = Eigen::SparseMatrix<FloatType, Eigen::RowMajor>;
  // vector (col major)
  using VectorXx = Eigen::Matrix<FloatType, Eigen::Dynamic, 1, Eigen::ColMajor>;
 
  ClassicalIsing(const graph::Spins &init_spin,
                 const graph::CSRSparse<FloatType> &init_interaction)
      : spin(utility::gen_vector_from_std_vector<FloatType, Eigen::ColMajor>(
            init_spin)),
        interaction(init_interaction.get_interactions()),
        num_spins(init_interaction.get_num_spins()) {
    assert(init_spin.size() == init_interaction.get_num_spins());
    reset_dE();
  }
 
  void reset_spins(const graph::Spins &init_spin) {
    this->spin =
        utility::gen_vector_from_std_vector<FloatType, Eigen::ColMajor>(
            init_spin);
    reset_dE();
  }
 
  void reset_dE() {
    this->dE =
        -2.0 * this->spin.array() * (this->interaction * this->spin).array();
  }
 
  VectorXx spin;
 
  const SparseMatrixXx interaction;
 
  const std::size_t num_spins; // spin.size()-1
 
  VectorXx dE;
};
 
template <typename GraphType>
auto make_classical_ising(const graph::Spins &init_spin,
                          const GraphType &init_interaction) {
  return ClassicalIsing<GraphType>(init_spin, init_interaction);
}
 
} // namespace system
} // namespace openjij