Example
Multiindex MCMC

Defines a two-dimensional hierarchy of simple Gaussian models and applies Multiindex MCMC to it.


#include "MUQ/SamplingAlgorithms/SLMCMC.h"
#include "MUQ/SamplingAlgorithms/GreedyMLMCMC.h"
#include "MUQ/SamplingAlgorithms/MIMCMC.h"

#include "MUQ/Modeling/Distributions/Gaussian.h"
#include "MUQ/Modeling/Distributions/Density.h"

#include "MUQ/SamplingAlgorithms/MHKernel.h"
#include "MUQ/SamplingAlgorithms/MHProposal.h"
#include "MUQ/SamplingAlgorithms/CrankNicolsonProposal.h"
#include "MUQ/SamplingAlgorithms/SamplingProblem.h"
#include "MUQ/SamplingAlgorithms/SubsamplingMIProposal.h"

#include "MUQ/SamplingAlgorithms/MIComponentFactory.h"

#include <boost/property_tree/ptree.hpp>

namespace pt = boost::property_tree;
using namespace muq::Modeling;
using namespace muq::SamplingAlgorithms;
using namespace muq::Utilities;


#include "Problem.h"



/*class MySamplingProblem : public AbstractSamplingProblem {
public:
  MySamplingProblem(std::shared_ptr<muq::Modeling::ModPiece> const& targetIn)
   : AbstractSamplingProblem(Eigen::VectorXi::Constant(1,2), Eigen::VectorXi::Constant(1,2)),
     target(targetIn){}

  virtual ~MySamplingProblem() = default;


  virtual double LogDensity(std::shared_ptr<SamplingState> const& state) override {
    lastState = state;
    return target->Evaluate(state->state).at(0)(0);
  };

  virtual std::shared_ptr<SamplingState> QOI() override {
    assert (lastState != nullptr);
    return std::make_shared<SamplingState>(lastState->state, 1.0);
  }

private:
  std::shared_ptr<SamplingState> lastState = nullptr;

  std::shared_ptr<muq::Modeling::ModPiece> target;

};


class MyInterpolation : public MIInterpolation {
public:
  std::shared_ptr<SamplingState> Interpolate (std::shared_ptr<SamplingState> const& coarseProposal, std::shared_ptr<SamplingState> const& fineProposal) {
    return std::make_shared<SamplingState>(coarseProposal->state);
  }
};

class MyMIComponentFactory : public MIComponentFactory {
public:
  virtual std::shared_ptr<MCMCProposal> Proposal (std::shared_ptr<MultiIndex> const& index, std::shared_ptr<AbstractSamplingProblem> const& samplingProblem) override {
    pt::ptree pt;
    pt.put("BlockIndex",0);

    Eigen::VectorXd mu(2);
    mu << 1.0, 2.0;
    Eigen::MatrixXd cov(2,2);
    cov << 0.7, 0.6,
    0.6, 1.0;
    cov *= 20.0;

    auto prior = std::make_shared<Gaussian>(mu, cov);

    return std::make_shared<CrankNicolsonProposal>(pt, samplingProblem, prior);
  }

  virtual std::shared_ptr<MultiIndex> FinestIndex() override {
    auto index = std::make_shared<MultiIndex>(2);
    index->SetValue(0, 2);
    index->SetValue(1, 2);
    return index;
  }

  virtual std::shared_ptr<MCMCProposal> CoarseProposal (std::shared_ptr<MultiIndex> const& index,
                                                        std::shared_ptr<AbstractSamplingProblem> const& coarseProblem,
                                                           std::shared_ptr<SingleChainMCMC> const& coarseChain) override {
    pt::ptree ptProposal;
    ptProposal.put("BlockIndex",0);
    int subsampling = 5;
    ptProposal.put("subsampling", subsampling);
    return std::make_shared<SubsamplingMIProposal>(ptProposal, coarseProblem, coarseChain);
  }

  virtual std::shared_ptr<AbstractSamplingProblem> SamplingProblem (std::shared_ptr<MultiIndex> const& index) override {
    Eigen::VectorXd mu(2);
    mu << 1.0, 2.0;
    Eigen::MatrixXd cov(2,2);
    cov << 0.7, 0.6,
           0.6, 1.0;

    if (index->GetValue(0) == 0) {
      mu[0] *= 0.8;
    } else if (index->GetValue(0) == 1) {
      mu[0] *= 0.9;
    } else if (index->GetValue(0) == 2) {
      mu[0] *= 1.0;
    } else {
      std::cerr << "Sampling problem not defined!" << std::endl;
      assert (false);
    }
    if (index->GetValue(1) == 0) {
      mu[1] *= 0.8;
    } else if (index->GetValue(1) == 1) {
      mu[1] *= 0.9;
    } else if (index->GetValue(1) == 2) {
      mu[1] *= 1.0;
    } else {
      std::cerr << "Sampling problem not defined!" << std::endl;
      assert (false);
    }
    if (index->Max() == 0) {
      cov *= 1.5;
    } else if (index->Max() == 1) {
      cov *= 1.2;
    } else if (index->Max() == 2) {
      cov *= 1.0;
    } else {
      std::cerr << "Sampling problem not defined!" << std::endl;
      assert (false);
    }

    auto coarseTargetDensity = std::make_shared<Gaussian>(mu, cov)->AsDensity();
    return std::make_shared<MySamplingProblem>(coarseTargetDensity);
  }

  virtual std::shared_ptr<MIInterpolation> Interpolation (std::shared_ptr<MultiIndex> const& index) override {
    return std::make_shared<MyInterpolation>();
  }

  virtual Eigen::VectorXd StartingPoint (std::shared_ptr<MultiIndex> const& index) override {
    Eigen::VectorXd mu(2);
    mu << 1.0, 2.0;
    return mu;
  }

};*/


int main(){

  pt::ptree pt;

  pt.put("NumSamples", 1e4); // number of samples for single level MCMC
  pt.put("NumSamples_0_0", 1e5);
  pt.put("NumSamples_0_1", 1e5);
  pt.put("NumSamples_0_2", 1e4);
  pt.put("NumSamples_1_0", 1e5);
  pt.put("NumSamples_1_1", 1e4);
  pt.put("NumSamples_1_2", 1e3);
  pt.put("NumSamples_2_0", 1e4);
  pt.put("NumSamples_2_1", 1e3);
  pt.put("NumSamples_2_2", 1e3);
  pt.put("MLMCMC.Subsampling", 5);

  auto componentFactory = std::make_shared<MyMIComponentFactory>(pt);


  std::cout << std::endl << "*************** multiindex chain" << std::endl << std::endl;

  MIMCMC mimcmc (pt, componentFactory);
  mimcmc.Run();
  mimcmc.Draw(false);
  std::cout << "mean QOI: " << mimcmc.MeanQOI().transpose() << std::endl;

  std::cout << std::endl << "*************** single chain reference" << std::endl << std::endl;

  SLMCMC slmcmc (pt, componentFactory);
  slmcmc.Run();
  std::cout << "mean QOI: " << slmcmc.MeanQOI().transpose() << std::endl;

  return 0;
}

Complete Code

#include "MUQ/SamplingAlgorithms/SLMCMC.h"
#include "MUQ/SamplingAlgorithms/GreedyMLMCMC.h"
#include "MUQ/SamplingAlgorithms/MIMCMC.h"

#include "MUQ/Modeling/Distributions/Gaussian.h"
#include "MUQ/Modeling/Distributions/Density.h"

#include "MUQ/SamplingAlgorithms/MHKernel.h"
#include "MUQ/SamplingAlgorithms/MHProposal.h"
#include "MUQ/SamplingAlgorithms/CrankNicolsonProposal.h"
#include "MUQ/SamplingAlgorithms/SamplingProblem.h"
#include "MUQ/SamplingAlgorithms/SubsamplingMIProposal.h"

#include "MUQ/SamplingAlgorithms/MIComponentFactory.h"

#include <boost/property_tree/ptree.hpp>

namespace pt = boost::property_tree;
using namespace muq::Modeling;
using namespace muq::SamplingAlgorithms;
using namespace muq::Utilities;


#include "Problem.h"



/*class MySamplingProblem : public AbstractSamplingProblem {
public:
  MySamplingProblem(std::shared_ptr<muq::Modeling::ModPiece> const& targetIn)
   : AbstractSamplingProblem(Eigen::VectorXi::Constant(1,2), Eigen::VectorXi::Constant(1,2)),
     target(targetIn){}

  virtual ~MySamplingProblem() = default;


  virtual double LogDensity(std::shared_ptr<SamplingState> const& state) override {
    lastState = state;
    return target->Evaluate(state->state).at(0)(0);
  };

  virtual std::shared_ptr<SamplingState> QOI() override {
    assert (lastState != nullptr);
    return std::make_shared<SamplingState>(lastState->state, 1.0);
  }

private:
  std::shared_ptr<SamplingState> lastState = nullptr;

  std::shared_ptr<muq::Modeling::ModPiece> target;

};


class MyInterpolation : public MIInterpolation {
public:
  std::shared_ptr<SamplingState> Interpolate (std::shared_ptr<SamplingState> const& coarseProposal, std::shared_ptr<SamplingState> const& fineProposal) {
    return std::make_shared<SamplingState>(coarseProposal->state);
  }
};

class MyMIComponentFactory : public MIComponentFactory {
public:
  virtual std::shared_ptr<MCMCProposal> Proposal (std::shared_ptr<MultiIndex> const& index, std::shared_ptr<AbstractSamplingProblem> const& samplingProblem) override {
    pt::ptree pt;
    pt.put("BlockIndex",0);

    Eigen::VectorXd mu(2);
    mu << 1.0, 2.0;
    Eigen::MatrixXd cov(2,2);
    cov << 0.7, 0.6,
    0.6, 1.0;
    cov *= 20.0;

    auto prior = std::make_shared<Gaussian>(mu, cov);

    return std::make_shared<CrankNicolsonProposal>(pt, samplingProblem, prior);
  }

  virtual std::shared_ptr<MultiIndex> FinestIndex() override {
    auto index = std::make_shared<MultiIndex>(2);
    index->SetValue(0, 2);
    index->SetValue(1, 2);
    return index;
  }

  virtual std::shared_ptr<MCMCProposal> CoarseProposal (std::shared_ptr<MultiIndex> const& index,
                                                        std::shared_ptr<AbstractSamplingProblem> const& coarseProblem,
                                                           std::shared_ptr<SingleChainMCMC> const& coarseChain) override {
    pt::ptree ptProposal;
    ptProposal.put("BlockIndex",0);
    int subsampling = 5;
    ptProposal.put("subsampling", subsampling);
    return std::make_shared<SubsamplingMIProposal>(ptProposal, coarseProblem, coarseChain);
  }

  virtual std::shared_ptr<AbstractSamplingProblem> SamplingProblem (std::shared_ptr<MultiIndex> const& index) override {
    Eigen::VectorXd mu(2);
    mu << 1.0, 2.0;
    Eigen::MatrixXd cov(2,2);
    cov << 0.7, 0.6,
           0.6, 1.0;

    if (index->GetValue(0) == 0) {
      mu[0] *= 0.8;
    } else if (index->GetValue(0) == 1) {
      mu[0] *= 0.9;
    } else if (index->GetValue(0) == 2) {
      mu[0] *= 1.0;
    } else {
      std::cerr << "Sampling problem not defined!" << std::endl;
      assert (false);
    }
    if (index->GetValue(1) == 0) {
      mu[1] *= 0.8;
    } else if (index->GetValue(1) == 1) {
      mu[1] *= 0.9;
    } else if (index->GetValue(1) == 2) {
      mu[1] *= 1.0;
    } else {
      std::cerr << "Sampling problem not defined!" << std::endl;
      assert (false);
    }
    if (index->Max() == 0) {
      cov *= 1.5;
    } else if (index->Max() == 1) {
      cov *= 1.2;
    } else if (index->Max() == 2) {
      cov *= 1.0;
    } else {
      std::cerr << "Sampling problem not defined!" << std::endl;
      assert (false);
    }

    auto coarseTargetDensity = std::make_shared<Gaussian>(mu, cov)->AsDensity();
    return std::make_shared<MySamplingProblem>(coarseTargetDensity);
  }

  virtual std::shared_ptr<MIInterpolation> Interpolation (std::shared_ptr<MultiIndex> const& index) override {
    return std::make_shared<MyInterpolation>();
  }

  virtual Eigen::VectorXd StartingPoint (std::shared_ptr<MultiIndex> const& index) override {
    Eigen::VectorXd mu(2);
    mu << 1.0, 2.0;
    return mu;
  }

};*/


int main(){

  pt::ptree pt;

  pt.put("NumSamples", 1e4); // number of samples for single level MCMC
  pt.put("NumSamples_0_0", 1e5);
  pt.put("NumSamples_0_1", 1e5);
  pt.put("NumSamples_0_2", 1e4);
  pt.put("NumSamples_1_0", 1e5);
  pt.put("NumSamples_1_1", 1e4);
  pt.put("NumSamples_1_2", 1e3);
  pt.put("NumSamples_2_0", 1e4);
  pt.put("NumSamples_2_1", 1e3);
  pt.put("NumSamples_2_2", 1e3);
  pt.put("MLMCMC.Subsampling", 5);

  auto componentFactory = std::make_shared<MyMIComponentFactory>(pt);


  std::cout << std::endl << "*************** multiindex chain" << std::endl << std::endl;

  MIMCMC mimcmc (pt, componentFactory);
  mimcmc.Run();
  mimcmc.Draw(false);
  std::cout << "mean QOI: " << mimcmc.MeanQOI().transpose() << std::endl;

  std::cout << std::endl << "*************** single chain reference" << std::endl << std::endl;

  SLMCMC slmcmc (pt, componentFactory);
  slmcmc.Run();
  std::cout << "mean QOI: " << slmcmc.MeanQOI().transpose() << std::endl;

  return 0;
}
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Acknowledgments

NSF Logo

This material is based upon work supported by the National Science Foundation under Grant No. 1550487.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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This material is based upon work supported by the US Department of Energy, Office of Advanced Scientific Computing Research, SciDAC (Scientific Discovery through Advanced Computing) program under awards DE-SC0007099 and DE-SC0021226, for the QUEST and FASTMath SciDAC Institutes.