include/openjij/updater/swendsen_wang.hpp
// 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 <algorithm>
#include <cmath>
#include <random>
#include <unordered_map>
#include "openjij/graph/graph.hpp"
#include "openjij/system/classical_ising.hpp"
#include "openjij/utility/schedule_list.hpp"
#include "openjij/utility/union_find.hpp"
namespace openjij {
namespace updater {
/**
* @brief swendsen wang updater
*
* @tparam System
*/
template <typename System> struct SwendsenWang;
/**
* @brief swendsen wang updater for classical ising model (on Sparse graph)
*
* @tparam FloatType
*/
template <typename FloatType>
struct SwendsenWang<system::ClassicalIsing<graph::Sparse<FloatType>>> {
using ClIsing = system::ClassicalIsing<graph::Sparse<FloatType>>;
template <typename RandomNumberEngine>
inline static void
update(ClIsing &system, RandomNumberEngine &random_number_engine,
const utility::ClassicalUpdaterParameter ¶meter) {
auto urd = std::uniform_real_distribution<>(0, 1.0);
// num_spin = system size + additional spin
const size_t num_spin = system.spin.size();
// 1. update bonds
auto union_find_tree = utility::UnionFind(num_spin);
for (std::size_t node = 0; node < num_spin; ++node) {
for (typename ClIsing::SparseMatrixXx::InnerIterator it(
system.interaction, node);
it; ++it) {
// fetch adjacent node
std::size_t adj_node = it.index();
// fetch system.interaction(node, adj_node)
const FloatType &J = it.value();
if (node >= adj_node)
continue;
// check if bond can be connected
if (J * system.spin(node) * system.spin(adj_node) > 0)
continue;
const auto unite_rate =
std::max(static_cast<FloatType>(0.0),
static_cast<FloatType>(
1.0 - std::exp(-2.0 * parameter.beta * std::abs(J))));
if (urd(random_number_engine) < unite_rate)
union_find_tree.unite_sets(node, adj_node);
}
}
// 2. make clusters
const auto cluster_map = [num_spin, &union_find_tree]() {
auto cluster_map = std::unordered_multimap<utility::UnionFind::Node,
utility::UnionFind::Node>();
for (std::size_t node = 0; node < num_spin; ++node) {
cluster_map.insert({union_find_tree.find_set(node), node});
}
return cluster_map;
}();
// 3. update spin states in each cluster
for (auto &&c : union_find_tree.get_roots()) {
const auto range = cluster_map.equal_range(c);
// 3.1. decide spin state (flip with the probability 1/2)
const FloatType probability = 1.0 / 2.0;
if (urd(random_number_engine) < probability) {
// 3.2. update spin states
for (auto itr = range.first, last = range.second; itr != last; ++itr) {
const auto idx = itr->second;
system.spin(idx) *= -1;
}
}
}
return;
}
};
/**
* @brief swendsen wang updater for classical ising model (on CSR Sparse graph)
*
* @tparam FloatType
*/
template <typename FloatType>
struct SwendsenWang<system::ClassicalIsing<graph::CSRSparse<FloatType>>> {
//TODO: duplicate code of `SwendsenWang<system::ClassicalIsing<graph::Sparse<FloatType>>>`, need fix.
using ClIsing = system::ClassicalIsing<graph::CSRSparse<FloatType>>;
template <typename RandomNumberEngine>
inline static void
update(ClIsing &system, RandomNumberEngine &random_number_engine,
const utility::ClassicalUpdaterParameter ¶meter) {
auto urd = std::uniform_real_distribution<>(0, 1.0);
// num_spin = system size + additional spin
const size_t num_spin = system.spin.size();
// 1. update bonds
auto union_find_tree = utility::UnionFind(num_spin);
for (std::size_t node = 0; node < num_spin; ++node) {
for (typename ClIsing::SparseMatrixXx::InnerIterator it(
system.interaction, node);
it; ++it) {
// fetch adjacent node
std::size_t adj_node = it.index();
// fetch system.interaction(node, adj_node)
const FloatType &J = it.value();
if (node >= adj_node)
continue;
// check if bond can be connected
if (J * system.spin(node) * system.spin(adj_node) > 0)
continue;
const auto unite_rate =
std::max(static_cast<FloatType>(0.0),
static_cast<FloatType>(
1.0 - std::exp(-2.0 * parameter.beta * std::abs(J))));
if (urd(random_number_engine) < unite_rate)
union_find_tree.unite_sets(node, adj_node);
}
}
// 2. make clusters
const auto cluster_map = [num_spin, &union_find_tree]() {
auto cluster_map = std::unordered_multimap<utility::UnionFind::Node,
utility::UnionFind::Node>();
for (std::size_t node = 0; node < num_spin; ++node) {
cluster_map.insert({union_find_tree.find_set(node), node});
}
return cluster_map;
}();
// 3. update spin states in each cluster
for (auto &&c : union_find_tree.get_roots()) {
const auto range = cluster_map.equal_range(c);
// 3.1. decide spin state (flip with the probability 1/2)
const FloatType probability = 1.0 / 2.0;
if (urd(random_number_engine) < probability) {
// 3.2. update spin states
for (auto itr = range.first, last = range.second; itr != last; ++itr) {
const auto idx = itr->second;
system.spin(idx) *= -1;
}
}
}
return;
}
};
} // namespace updater
} // namespace openjij