Acts/Utilities/AnnealingUtility.hpp

0001 // This file is part of the Acts project.
0002 //
0003 // Copyright (C) 2019 CERN for the benefit of the Acts project
0004 //
0005 // This Source Code Form is subject to the terms of the Mozilla Public
0006 // License, v. 2.0. If a copy of the MPL was not distributed with this
0007 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
0008
0009 #pragma once
0010
0011 #include "Acts/Definitions/Algebra.hpp"
0012
0013 #include <cmath>
0014 #include <vector>
0015
0016 namespace Acts {
0017 /// @brief Implements a deterministic thermodynamic annealing scheme
0018 /// Ref. (1): CERN-THESIS-2010-027
0019 class AnnealingUtility {
0020  public:
0021   /// @brief The annealing state
0022   /// Resetting the state is done by just creating a new instance
0023   struct State {
0024     // Points to current temperature value in m_cfg.setOfTemperatures
0025     unsigned int currentTemperatureIndex{0};
0026
0027     // Checks if equilibrium is reached
0028     bool equilibriumReached{false};
0029   };
0030
0031   /// @brief The configuration struct
0032   struct Config {
0033     Config();
0034
0035     // Insensitivity of calculated weight at cutoff
0036     double cutOff{9.};
0037
0038     // Set of temperatures, annealing starts at setOfTemperatures[0]
0039     // and anneals towards setOfTemperatures[last]
0040     std::vector<double> setOfTemperatures{64., 16., 4., 2., 1.5, 1.};
0041   };
0042
0043   /// Constructor
0044   AnnealingUtility(const Config& cfg = Config()) : m_cfg(cfg) {
0045     // Set Gaussian cut-off terms for each temperature
0046     for (double temp : cfg.setOfTemperatures) {
0047       m_gaussCutTempVec.push_back(std::exp(-cfg.cutOff / (2. * temp)));
0048     }
0049   }
0050
0051   /// Does the actual annealing step
0052   void anneal(State& state) const;
0053
0054   /// @brief Weight access
0055   ///
0056   /// @param state The state object
0057   /// @param chi2 Chi^2 for e.g. current track, i.e. compatibility
0058   /// of track to current vertex candidate
0059   /// @param allChi2 Vector of all chi^2 values, i.e. e.g. compatibilities
0060   /// of current track to all vertices it is currently attached to
0061   ///
0062   /// @return Calculated weight according to Eq.(5.46) in Ref.(1)
0063   double getWeight(State& state, double chi2,
0064                    const std::vector<double>& allChi2) const;
0065
0066   /// @brief Weight access
0067   ///
0068   /// @param state The state object
0069   /// @param chi2 Chi^2
0070   ///
0071   /// @return Calculated weight
0072   double getWeight(State& state, double chi2) const;
0073
0074  private:
0075   /// Configuration object
0076   Config m_cfg;
0077
0078   // For each temperature, a Gaussian term with the chi2 cut-off value
0079   // is calculated and stored here
0080   std::vector<double> m_gaussCutTempVec;
0081 };
0082 }  // namespace Acts