AnnealingUtility.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2019 CERN for the benefit of the Acts project
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#pragma once

#include "Acts/Definitions/Algebra.hpp"

#include <cmath>
#include <vector>

namespace Acts {
class AnnealingUtility {
 public:
  struct State {
    // Points to current temperature value in m_cfg.setOfTemperatures
    unsigned int currentTemperatureIndex{0};

    // Checks if equilibrium is reached
    bool equilibriumReached{false};
  };

  struct Config {
    Config();

    // Insensitivity of calculated weight at cutoff
    double cutOff{9.};

    // Set of temperatures, annealing starts at setOfTemperatures[0]
    // and anneals towards setOfTemperatures[last]
    std::vector<double> setOfTemperatures{64., 16., 4., 2., 1.5, 1.};
  };

  AnnealingUtility(const Config& cfg = Config()) : m_cfg(cfg) {
    // Set Gaussian cut-off terms for each temperature
    for (double temp : cfg.setOfTemperatures) {
      m_gaussCutTempVec.push_back(std::exp(-cfg.cutOff / (2. * temp)));
    }
  }

  void anneal(State& state) const;

  double getWeight(State& state, double chi2,
                   const std::vector<double>& allChi2) const;

  double getWeight(State& state, double chi2) const;

 private:
  Config m_cfg;

  // For each temperature, a Gaussian term with the chi2 cut-off value
  // is calculated and stored here
  std::vector<double> m_gaussCutTempVec;
};
}  // namespace Acts