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HowToUseMonteCarloSimulation.md

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How To Use Monte Carlo Simulation

1. Overview

  • S2E has a framework to execute the Monte Carlo Simulation.
  • The feature provides a framework to randomize arbitrary parameters in each class.
  • Users can set the mean value and standard deviation for the randomized parameters with simulation_base.ini file of each user.
  • This tutorial explains how to randomly change the initial value of the spacecraft angular velocity.
  • The supported version of this document
    • Please confirm that the version of the documents and s2e-core is compatible.

2. Edit Simulation Case

  • To use the Monte Carlo simulation, users have to edit their user_case.hpp and user_case.cpp
  • user_case.hpp
    • Add header including 
      #include <./simulation/monte_carlo_simulation/monte_carlo_simulation_executor.hpp>
    • Add private member variables for MonteCarloSimulationExecutor. 
      MonteCarloSimulationExecutor &monte_carlo_simulator_;
    • Replace the constructor of UserCase class to add arguments for Monte Carlo simulation. 
      UserCase(const std::string initialize_base_file, MonteCarloSimulationExecutor &monte_carlo_simulator, const std::string log_path);
  • user_case.cpp
    • Add header including 
      #include <./simulation/monte_carlo_simulation/simulation_object.hpp>
    • Replace the constructor as follows 
      UserCase::UserCase(const std::string initialize_base_file, MonteCarloSimulationExecutor &monte_carlo_simulator, const std::string log_path)
: SimulationCase(initialize_base_file, monte_carlo_simulator, log_path), monte_carlo_simulator_(monte_carlo_simulator) {}
    • Edit InitializeTargetObjects function
      • Edit log file name definition and
      • Add MonteCarloSimulationExecutor initialization 
        // Monte Carlo Simulation
monte_carlo_simulator_.SetSeed();
monte_carlo_simulator_.RandomizeAllParameters();
SimulationObject::SetAllParameters(monte_carlo_simulator_);
monte_carlo_simulator_.AtTheBeginningOfEachCase();
    • Add log settings for the Monte Carlo simulation
      • The GetLogHeader and GetLogValue functions are used for Monte Carlo log output.
        • The log output defined in the function is executed at the beginning and end of a simulation case.
        • The output line will be 2N+1, where N is the sample number of the Monte Carlo simulation.
          • +1 line is for headers.
      • In this tutorial, time, angular velocity, and quaternion are logged.
        • Users can customize this output depending on their needs.
        std::string UserCase::GetLogHeader() const
{
  std::string str_tmp = "";

  str_tmp += WriteScalar("elapsed_time", "s");
  str_tmp += WriteVector("spacecraft_angular_velocity", "b", "rad/s", 3);
  str_tmp += WriteVector("spacecraft_quaternion", "i2b", "-", 4);

  return str_tmp;
}
std::string UserCase::GetLogValue() const
{
  std::string str_tmp = "";

  str_tmp += WriteScalar(global_environment_->GetSimulationTime().GetElapsedTime_s());
  str_tmp += WriteVector(spacecraft_->GetDynamics().GetAttitude().GetAngularVelocity_b_rad_s(), 3);
  str_tmp += WriteQuaternion(spacecraft_->GetDynamics().GetAttitude().GetQuaternion_i2b());

  return str_tmp;
}

3. Edit s2e_user.cpp code

  • To use the Monte Carlo Simulator, users have to edit their s2e_user.cpp
  • Add header file 
    #include <./simulation/monte_carlo_simulation/initialize_monte_carlo_simulation.hpp>
  • If you find description below 
    #include "library/logger/logger.hpp"
    rewrite as the following description 
    #include "library/logger/initialize_log.hpp"
  • Make an instance of MonteCarloSimulatorExecutor and Logger for Monte Carlo log 
    MonteCarloSimulationExecutor *mc_simulator = InitMonteCarloSimulation(ini_file);
Logger *log_mc_sim = InitMonteCarloLog(ini_file, mc_simulator->IsEnabled());
  • Add while loop for Monte Carlo simulation as follows 
    while (mc_simulator->WillExecuteNextCase()) {
  auto simulation_case = UserCase(ini_file, *mc_simulator);
  // Initialize
  log_mc_simulator->AddLogList(&simulation_case);
  if (mc_simulator->GetNumberOfExecutionsDone() == 0) log_mc_simulator->WriteHeaders();
  simulation_case.Initialize();
  // Main
  log_mc_simulator->WriteValues();  // log initial value
  simulation_case.Main();
  mc_simulator->AtTheEndOfEachCase();
  log_mc_simulator->WriteValues();  // log final value
  log_mc_simulator->ClearLogList();
}

delete log_mc_simulator;
delete mc_simulator;

4. Initialize file for Monte Carlo simulator

  • Edit user_simulation_base.ini to add the following description

    [MONTE_CARLO_EXECUTION]
// Whether Monte-Carlo Simulation is executed or not
monte_carlo_enable = ENABLE

// Whether you want output the log file for each step
log_enable = ENABLE

// Number of execution
number_of_executions = 3

[MONTE_CARLO_RANDOMIZATION]
parameter(0) = attitude0.angular_velocity_b_rad_s
attitude0.angular_velocity_b_rad_s.randomization_type = CartesianUniform
attitude0.angular_velocity_b_rad_s.mean_or_min(0) = 0.0
attitude0.angular_velocity_b_rad_s.mean_or_min(1) = 0.0
attitude0.angular_velocity_b_rad_s.mean_or_min(2) = 0.0
attitude0.angular_velocity_b_rad_s.sigma_or_max(0) = 0.05817764 // 3-sigma = 10 [deg/s]
attitude0.angular_velocity_b_rad_s.sigma_or_max(1) = 0.05817764 // 3-sigma = 10 [deg/s]
attitude0.angular_velocity_b_rad_s.sigma_or_max(2) = 0.05817764 // 3-sigma = 10 [deg/s]

  • You can set the following parameters

    • monte_carlo_enable:
      • ENABLE: S2E executes the Monte Carlo Simulation.
      • DISABLE: S2E executes a simulation case defined in ini files.
    • log_enable:
      • ENABLE: A default csv log file is outputted for each sample case.
        • Note: 100 csv files will be generated when you set number_of_executions = 100.
      • DISABLE: No default csv log file will be generated. Only a monte_carlo csv log file will be generated.
        • Note: When monte_carlo_enable = DISABLE, a default csv log file will always be generated.
    • number_of_executions: integer lager than 1
      • The total calculation time is proportional to this value.

  • Randomized parameters

    • randomization_type: You can choose the randomization type. See Monte Carlo Simulation for detail.
    • mean_or_min: Input mean value or minimum value. (Depends on Randomization type)
    • sigma_or_max: Input standard deviation or maximum value. (Depends on Randomization type)

6. Execute and check logs

  • Build the S2E_USER and execute it.
  • In the data directory, you can find one xxxx_monte_carlo.csv file and several xxxx_default.csv files, which depend on your Monte Carlo Simulator setting.
  • The initial value of angular velocity is randomly varied by the Monte Carlo Simulator.