HybridMinimizer.cc

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// @(#)root/minuit2:$Id$
// Author: L. Moneta Wed Oct 18 11:48:00 2006

/**********************************************************************
 *                                                                    *
 * Copyright (c) 2006  LCG ROOT Math Team, CERN/PH-SFT                *
 *                                                                    *
 *                                                                    *
 **********************************************************************/

// by lhx: Note copied and modifed from the Minuit2Minimizer to suit our purpose
// Changes mainly to make the SetMinimizerType public so that user can re-new to
// different minimizer...
// Implementation file for class HybridMinimizer

#include "RecoLocalCalo/HcalRecAlgos/src/HybridMinimizer.h"

#include "Math/IFunction.h"
#include "Math/IOptions.h"

#include "Minuit2/FCNAdapter.h"
#include "Minuit2/FumiliFCNAdapter.h"
#include "Minuit2/FCNGradAdapter.h"
#include "Minuit2/FunctionMinimum.h"
#include "Minuit2/MnMigrad.h"
#include "Minuit2/MnMinos.h"
#include "Minuit2/MinosError.h"
#include "Minuit2/MnHesse.h"
#include "Minuit2/MinuitParameter.h"
#include "Minuit2/MnUserFcn.h"
#include "Minuit2/MnPrint.h"
#include "Minuit2/FunctionMinimum.h"
#include "Minuit2/VariableMetricMinimizer.h"
#include "Minuit2/SimplexMinimizer.h"
#include "Minuit2/CombinedMinimizer.h"
#include "Minuit2/ScanMinimizer.h"
#include "Minuit2/FumiliMinimizer.h"
#include "Minuit2/MnParameterScan.h"
#include "Minuit2/MnContours.h"

#include <cassert>
#include <iostream>
#include <algorithm>
#include <functional>

namespace PSFitter {

  using namespace ROOT::Minuit2;

  // functions needed to control siwthc off of Minuit2 printing level
#ifdef USE_ROOT_ERROR
  int TurnOffPrintInfoLevel() {
    // switch off Minuit2 printing of INFO message (cut off is 1001)
    int prevErrorIgnoreLevel = gErrorIgnoreLevel;
    if (prevErrorIgnoreLevel < 1001) {
      gErrorIgnoreLevel = 1001;
      return prevErrorIgnoreLevel;
    }
    return -2;  // no op in this case
  }

  void RestoreGlobalPrintLevel(int value) { gErrorIgnoreLevel = value; }
#else
  // dummy functions
  int TurnOffPrintInfoLevel() { return -1; }
  int ControlPrintLevel() { return -1; }
  void RestoreGlobalPrintLevel(int) {}
#endif

  HybridMinimizer::HybridMinimizer(EMinimizerType type)
      : Minimizer(), fDim(0), fMinimizer(nullptr), fMinuitFCN(nullptr), fMinimum(nullptr) {
    // Default constructor implementation depending on minimizer type
    SetMinimizerType(type);
  }

  HybridMinimizer::HybridMinimizer(const char *type)
      : Minimizer(), fDim(0), fMinimizer(nullptr), fMinuitFCN(nullptr), fMinimum(nullptr) {
    // constructor from a string

    std::string algoname(type);
    // tolower() is not an  std function (Windows)
    std::transform(algoname.begin(), algoname.end(), algoname.begin(), (int (*)(int))tolower);

    EMinimizerType algoType = kMigrad;
    if (algoname == "simplex")
      algoType = kSimplex;
    if (algoname == "minimize")
      algoType = kCombined;
    if (algoname == "scan")
      algoType = kScan;
    if (algoname == "fumili")
      algoType = kFumili;

    SetMinimizerType(algoType);
  }

  void HybridMinimizer::SetMinimizerType(EMinimizerType type) {
    // Set  minimizer algorithm type
    fUseFumili = false;

    if (fMinimizer)
      delete fMinimizer;

    switch (type) {
      case kMigrad:
        //std::cout << "HybridMinimizer: minimize using MIGRAD " << std::endl;
        SetMinimizer(new ROOT::Minuit2::VariableMetricMinimizer());
        return;
      case kSimplex:
        //std::cout << "HybridMinimizer: minimize using SIMPLEX " << std::endl;
        SetMinimizer(new ROOT::Minuit2::SimplexMinimizer());
        return;
      case kCombined:
        SetMinimizer(new ROOT::Minuit2::CombinedMinimizer());
        return;
      case kScan:
        SetMinimizer(new ROOT::Minuit2::ScanMinimizer());
        return;
      case kFumili:
        SetMinimizer(new ROOT::Minuit2::FumiliMinimizer());
        fUseFumili = true;
        return;
      default:
        //migrad minimizer
        SetMinimizer(new ROOT::Minuit2::VariableMetricMinimizer());
    }
  }

  HybridMinimizer::~HybridMinimizer() {
    // Destructor implementation.
    if (fMinimizer)
      delete fMinimizer;
    if (fMinuitFCN)
      delete fMinuitFCN;
    if (fMinimum)
      delete fMinimum;
  }

  HybridMinimizer::HybridMinimizer(const HybridMinimizer &) : ROOT::Math::Minimizer() {
    // Implementation of copy constructor.
  }

  HybridMinimizer &HybridMinimizer::operator=(const HybridMinimizer &rhs) {
    // Implementation of assignment operator.
    if (this == &rhs)
      return *this;  // time saving self-test
    return *this;
  }

  void HybridMinimizer::Clear() {
    // delete the state in case of consecutive minimizations
    fState = MnUserParameterState();
    // clear also the function minimum
    if (fMinimum)
      delete fMinimum;
    fMinimum = nullptr;
  }

  // set variables

  bool HybridMinimizer::SetVariable(unsigned int ivar, const std::string &name, double val, double step) {
    // set a free variable.
    // Add the variable if not existing otherwise  set value if exists already
    // this is implemented in MnUserParameterState::Add
    // if index is wrong (i.e. variable already exists but with a different index return false) but
    // value is set for corresponding variable name

    //    std::cout << " add parameter " << name << "  " <<  val << " step " << step << std::endl;

    if (step <= 0) {
      std::string txtmsg = "Parameter " + name + "  has zero or invalid step size - consider it as constant ";
      MN_INFO_MSG2("HybridMinimizer::SetVariable", txtmsg);
      fState.Add(name, val);
    } else
      fState.Add(name, val, step);

    unsigned int minuit2Index = fState.Index(name);
    if (minuit2Index != ivar) {
      std::string txtmsg("Wrong index used for the variable " + name);
      MN_INFO_MSG2("HybridMinimizer::SetVariable", txtmsg);
      MN_INFO_VAL2("HybridMinimizer::SetVariable", minuit2Index);
      return false;
    }
    fState.RemoveLimits(ivar);

    return true;
  }

  bool HybridMinimizer::SetLowerLimitedVariable(
      unsigned int ivar, const std::string &name, double val, double step, double lower) {
    // add a lower bounded variable
    if (!SetVariable(ivar, name, val, step))
      return false;
    fState.SetLowerLimit(ivar, lower);
    return true;
  }

  bool HybridMinimizer::SetUpperLimitedVariable(
      unsigned int ivar, const std::string &name, double val, double step, double upper) {
    // add a upper bounded variable
    if (!SetVariable(ivar, name, val, step))
      return false;
    fState.SetUpperLimit(ivar, upper);
    return true;
  }

  bool HybridMinimizer::SetLimitedVariable(
      unsigned int ivar, const std::string &name, double val, double step, double lower, double upper) {
    // add a double bound variable
    if (!SetVariable(ivar, name, val, step))
      return false;
    fState.SetLimits(ivar, lower, upper);
    return true;
  }

  bool HybridMinimizer::SetFixedVariable(unsigned int ivar, const std::string &name, double val) {
    // add a fixed variable
    // need a step size otherwise treated as a constant
    // use 10%
    double step = (val != 0) ? 0.1 * std::abs(val) : 0.1;
    if (!SetVariable(ivar, name, val, step)) {
      ivar = fState.Index(name);
    }
    fState.Fix(ivar);
    return true;
  }

  std::string HybridMinimizer::VariableName(unsigned int ivar) const {
    // return the variable name
    if (ivar >= fState.MinuitParameters().size())
      return std::string();
    return fState.GetName(ivar);
  }

  int HybridMinimizer::VariableIndex(const std::string &name) const {
    // return the variable index
    // check if variable exist
    return fState.Trafo().FindIndex(name);
  }

  bool HybridMinimizer::SetVariableValue(unsigned int ivar, double val) {
    // set value for variable ivar (only for existing parameters)
    if (ivar >= fState.MinuitParameters().size())
      return false;
    fState.SetValue(ivar, val);
    return true;
  }

  bool HybridMinimizer::SetVariableValues(const double *x) {
    // set value for variable ivar (only for existing parameters)
    unsigned int n = fState.MinuitParameters().size();
    if (n == 0)
      return false;
    for (unsigned int ivar = 0; ivar < n; ++ivar)
      fState.SetValue(ivar, x[ivar]);
    return true;
  }

  void HybridMinimizer::SetFunction(const ROOT::Math::IMultiGenFunction &func) {
    // set function to be minimized
    if (fMinuitFCN)
      delete fMinuitFCN;
    fDim = func.NDim();
    if (!fUseFumili) {
      fMinuitFCN = new ROOT::Minuit2::FCNAdapter<ROOT::Math::IMultiGenFunction>(func, ErrorDef());
    } else {
      // for Fumili the fit method function interface is required
      const ROOT::Math::FitMethodFunction *fcnfunc = dynamic_cast<const ROOT::Math::FitMethodFunction *>(&func);
      if (!fcnfunc) {
        MN_ERROR_MSG("HybridMinimizer: Wrong Fit method function for Fumili");
        return;
      }
      fMinuitFCN = new ROOT::Minuit2::FumiliFCNAdapter<ROOT::Math::FitMethodFunction>(*fcnfunc, fDim, ErrorDef());
    }
  }

  void HybridMinimizer::SetFunction(const ROOT::Math::IMultiGradFunction &func) {
    // set function to be minimized
    fDim = func.NDim();
    if (fMinuitFCN)
      delete fMinuitFCN;
    if (!fUseFumili) {
      fMinuitFCN = new ROOT::Minuit2::FCNGradAdapter<ROOT::Math::IMultiGradFunction>(func, ErrorDef());
    } else {
      // for Fumili the fit method function interface is required
      const ROOT::Math::FitMethodGradFunction *fcnfunc = dynamic_cast<const ROOT::Math::FitMethodGradFunction *>(&func);
      if (!fcnfunc) {
        MN_ERROR_MSG("HybridMinimizer: Wrong Fit method function for Fumili");
        return;
      }
      fMinuitFCN = new ROOT::Minuit2::FumiliFCNAdapter<ROOT::Math::FitMethodGradFunction>(*fcnfunc, fDim, ErrorDef());
    }
  }

  bool HybridMinimizer::Minimize() {
    // perform the minimization
    // store a copy of FunctionMinimum
    if (!fMinuitFCN) {
      MN_ERROR_MSG2("HybridMinimizer::Minimize", "FCN function has not been set");
      return false;
    }

    assert(GetMinimizer() != nullptr);

    // delete result of previous minimization
    if (fMinimum)
      delete fMinimum;
    fMinimum = nullptr;

    int maxfcn = MaxFunctionCalls();
    double tol = Tolerance();
    int strategyLevel = Strategy();
    fMinuitFCN->SetErrorDef(ErrorDef());

    /*
   if (PrintLevel() >=1) { 
      // print the real number of maxfcn used (defined in ModularFuncitonMinimizer)
      int maxfcn_used = maxfcn; 
      if (maxfcn_used == 0) { 
    int nvar = fState.VariableParameters();
    maxfcn_used = 200 + 100*nvar + 5*nvar*nvar;
      }      
//      std::cout << "HybridMinimizer: Minimize with max-calls " << maxfcn_used 
//                << " convergence for edm < " << tol << " strategy " 
//                << strategyLevel << std::endl; 
   }
   */

    // internal minuit messages
    MnPrint::SetLevel(PrintLevel());

    // switch off Minuit2 printing
    int prev_level = (PrintLevel() <= 0) ? TurnOffPrintInfoLevel() : -2;

    // set the precision if needed
    if (Precision() > 0)
      fState.SetPrecision(Precision());

    // set strategy and add extra options if needed
    ROOT::Minuit2::MnStrategy strategy(strategyLevel);
    ROOT::Math::IOptions *minuit2Opt = ROOT::Math::MinimizerOptions::FindDefault("Minuit2");
    if (minuit2Opt) {
      // set extra strategy options
      int nGradCycles = strategy.GradientNCycles();
      int nHessCycles = strategy.HessianNCycles();
      int nHessGradCycles = strategy.HessianGradientNCycles();

      double gradTol = strategy.GradientTolerance();
      double gradStepTol = strategy.GradientStepTolerance();
      double hessStepTol = strategy.HessianStepTolerance();
      double hessG2Tol = strategy.HessianG2Tolerance();

      minuit2Opt->GetValue("GradientNCycles", nGradCycles);
      minuit2Opt->GetValue("HessianNCycles", nHessCycles);
      minuit2Opt->GetValue("HessianGradientNCycles", nHessGradCycles);

      minuit2Opt->GetValue("GradientTolerance", gradTol);
      minuit2Opt->GetValue("GradientStepTolerance", gradStepTol);
      minuit2Opt->GetValue("HessianStepTolerance", hessStepTol);
      minuit2Opt->GetValue("HessianG2Tolerance", hessG2Tol);

      strategy.SetGradientNCycles(nGradCycles);
      strategy.SetHessianNCycles(nHessCycles);
      strategy.SetHessianGradientNCycles(nHessGradCycles);

      strategy.SetGradientTolerance(gradTol);
      strategy.SetGradientStepTolerance(gradStepTol);
      strategy.SetHessianStepTolerance(hessStepTol);
      strategy.SetHessianG2Tolerance(hessStepTol);

      if (PrintLevel() > 0) {
        //         std::cout << "HybridMinimizer::Minuit  - Changing default stratgey options" << std::endl;
        minuit2Opt->Print();
      }
    }

    const ROOT::Minuit2::FCNGradientBase *gradFCN = dynamic_cast<const ROOT::Minuit2::FCNGradientBase *>(fMinuitFCN);
    if (gradFCN != nullptr) {
      // use gradient
      //SetPrintLevel(3);
      ROOT::Minuit2::FunctionMinimum min = GetMinimizer()->Minimize(*gradFCN, fState, strategy, maxfcn, tol);
      fMinimum = new ROOT::Minuit2::FunctionMinimum(min);
    } else {
      ROOT::Minuit2::FunctionMinimum min = GetMinimizer()->Minimize(*GetFCN(), fState, strategy, maxfcn, tol);
      fMinimum = new ROOT::Minuit2::FunctionMinimum(min);
    }

    // check if Hesse needs to be run
    if (fMinimum->IsValid() && IsValidError() && fMinimum->State().Error().Dcovar() != 0) {
      // run Hesse (Hesse will add results in the last state of fMinimum
      ROOT::Minuit2::MnHesse hesse(strategy);
      hesse(*fMinuitFCN, *fMinimum, maxfcn);
    }

    // -2 is the highest low invalid value for gErrorIgnoreLevel
    if (prev_level > -2)
      RestoreGlobalPrintLevel(prev_level);

    fState = fMinimum->UserState();
    bool ok = ExamineMinimum(*fMinimum);
    //fMinimum = 0;
    return ok;
  }

  bool HybridMinimizer::ExamineMinimum(const ROOT::Minuit2::FunctionMinimum &min) {

    // debug ( print all the states)
    int debugLevel = PrintLevel();
    if (debugLevel >= 3) {
      /*      
      const std::vector<ROOT::Minuit2::MinimumState>& iterationStates = min.States();
      std::cout << "Number of iterations " << iterationStates.size() << std::endl;
      for (unsigned int i = 0; i <  iterationStates.size(); ++i) {
         //std::cout << iterationStates[i] << std::endl;                                                                       
         const ROOT::Minuit2::MinimumState & st =  iterationStates[i];
         std::cout << "----------> Iteration " << i << std::endl;
         int pr = std::cout.precision(12);
         std::cout << "            FVAL = " << st.Fval() << " Edm = " << st.Edm() << " Nfcn = " << st.NFcn() << std::endl;
         std::cout.precision(pr);
         std::cout << "            Error matrix change = " << st.Error().Dcovar() << std::endl;
         std::cout << "            Parameters : ";
         // need to transform from internal to external 
         for (int j = 0; j < st.size() ; ++j) std::cout << " p" << j << " = " << fState.Int2ext( j, st.Vec()(j) );
         std::cout << std::endl;
      }
*/
    }

    fStatus = 0;
    std::string txt;
    if (min.HasMadePosDefCovar()) {
      txt = "Covar was made pos def";
      fStatus = 1;
    }
    if (min.HesseFailed()) {
      txt = "Hesse is not valid";
      fStatus = 2;
    }
    if (min.IsAboveMaxEdm()) {
      txt = "Edm is above max";
      fStatus = 3;
    }
    if (min.HasReachedCallLimit()) {
      txt = "Reached call limit";
      fStatus = 4;
    }

    bool validMinimum = min.IsValid();
    if (validMinimum) {
      // print a warning message in case something is not ok
      if (fStatus != 0 && debugLevel > 0)
        MN_INFO_MSG2("HybridMinimizer::Minimize", txt);
    } else {
      // minimum is not valid when state is not valid and edm is over max or has passed call limits
      if (fStatus == 0) {
        // this should not happen
        txt = "unknown failure";
        fStatus = 5;
      }
      std::string msg = "Minimization did NOT converge, " + txt;
      MN_INFO_MSG2("HybridMinimizer::Minimize", msg);
    }

    if (debugLevel >= 1)
      PrintResults();
    return validMinimum;
  }

  void HybridMinimizer::PrintResults() {
    // print results of minimization
    if (!fMinimum)
      return;
    if (fMinimum->IsValid()) {
      // valid minimum
      /*
      std::cout << "HybridMinimizer : Valid minimum - status = " << fStatus  << std::endl; 
      int pr = std::cout.precision(18);
      std::cout << "FVAL  = " << fState.Fval() << std::endl;
      std::cout << "Edm   = " << fState.Edm() << std::endl;
      std::cout.precision(pr);
      std::cout << "Nfcn  = " << fState.NFcn() << std::endl;
      for (unsigned int i = 0; i < fState.MinuitParameters().size(); ++i) {
         const MinuitParameter & par = fState.Parameter(i); 
         std::cout << par.Name() << "\t  = " << par.Value() << "\t ";
         if (par.IsFixed() )      std::cout << "(fixed)" << std::endl;
         else if (par.IsConst() ) std::cout << "(const)" << std::endl;
         else if (par.HasLimits() ) 
            std::cout << "+/-  " << par.Error() << "\t(limited)"<< std::endl; 
         else 
            std::cout << "+/-  " << par.Error() << std::endl; 
      }
*/
    } else {
      /*
      std::cout << "HybridMinimizer : Invalid Minimum - status = " << fStatus << std::endl; 
      std::cout << "FVAL  = " << fState.Fval() << std::endl;
      std::cout << "Edm   = " << fState.Edm() << std::endl;
      std::cout << "Nfcn  = " << fState.NFcn() << std::endl;
*/
    }
  }

  const double *HybridMinimizer::X() const {
    // return values at minimum
    const std::vector<MinuitParameter> &paramsObj = fState.MinuitParameters();
    if (paramsObj.empty())
      return nullptr;
    assert(fDim == paramsObj.size());
    // be careful for multiple calls of this function. I will redo an allocation here
    // only when size of vectors has changed (e.g. after a new minimization)
    if (fValues.size() != fDim)
      fValues.resize(fDim);
    for (unsigned int i = 0; i < fDim; ++i) {
      fValues[i] = paramsObj[i].Value();
    }

    return &fValues.front();
  }

  const double *HybridMinimizer::Errors() const {
    // return error at minimum (set to zero for fixed and constant params)
    const std::vector<MinuitParameter> &paramsObj = fState.MinuitParameters();
    if (paramsObj.empty())
      return nullptr;
    assert(fDim == paramsObj.size());
    // be careful for multiple calls of this function. I will redo an allocation here
    // only when size of vectors has changed (e.g. after a new minimization)
    if (fErrors.size() != fDim)
      fErrors.resize(fDim);
    for (unsigned int i = 0; i < fDim; ++i) {
      const MinuitParameter &par = paramsObj[i];
      if (par.IsFixed() || par.IsConst())
        fErrors[i] = 0;
      else
        fErrors[i] = par.Error();
    }

    return &fErrors.front();
  }

  double HybridMinimizer::CovMatrix(unsigned int i, unsigned int j) const {
    // get value of covariance matrices (transform from external to internal indices)
    if (i >= fDim || i >= fDim)
      return 0;
    if (!fState.HasCovariance())
      return 0;  // no info available when minimization has failed
    if (fState.Parameter(i).IsFixed() || fState.Parameter(i).IsConst())
      return 0;
    if (fState.Parameter(j).IsFixed() || fState.Parameter(j).IsConst())
      return 0;
    unsigned int k = fState.IntOfExt(i);
    unsigned int l = fState.IntOfExt(j);
    return fState.Covariance()(k, l);
  }

  bool HybridMinimizer::GetCovMatrix(double *cov) const {
    // get value of covariance matrices
    if (!fState.HasCovariance())
      return false;  // no info available when minimization has failed
    for (unsigned int i = 0; i < fDim; ++i) {
      if (fState.Parameter(i).IsFixed() || fState.Parameter(i).IsConst()) {
        for (unsigned int j = 0; j < fDim; ++j) {
          cov[i * fDim + j] = 0;
        }
      } else {
        unsigned int l = fState.IntOfExt(i);
        for (unsigned int j = 0; j < fDim; ++j) {
          // could probably speed up this loop (if needed)
          int k = i * fDim + j;
          if (fState.Parameter(j).IsFixed() || fState.Parameter(j).IsConst())
            cov[k] = 0;
          else {
            // need to transform from external to internal indices)
            // for taking care of the removed fixed row/columns in the Minuit2 representation
            unsigned int m = fState.IntOfExt(j);
            cov[k] = fState.Covariance()(l, m);
          }
        }
      }
    }
    return true;
  }

  bool HybridMinimizer::GetHessianMatrix(double *hess) const {
    // get value of Hessian matrix
    // this is the second derivative matrices
    if (!fState.HasCovariance())
      return false;  // no info available when minimization has failed
    for (unsigned int i = 0; i < fDim; ++i) {
      if (fState.Parameter(i).IsFixed() || fState.Parameter(i).IsConst()) {
        for (unsigned int j = 0; j < fDim; ++j) {
          hess[i * fDim + j] = 0;
        }
      } else {
        unsigned int l = fState.IntOfExt(i);
        for (unsigned int j = 0; j < fDim; ++j) {
          // could probably speed up this loop (if needed)
          int k = i * fDim + j;
          if (fState.Parameter(j).IsFixed() || fState.Parameter(j).IsConst())
            hess[k] = 0;
          else {
            // need to transform from external to internal indices)
            // for taking care of the removed fixed row/columns in the Minuit2 representation
            unsigned int m = fState.IntOfExt(j);
            hess[k] = fState.Hessian()(l, m);
          }
        }
      }
    }

    return true;
  }

  double HybridMinimizer::Correlation(unsigned int i, unsigned int j) const {
    // get correlation between parameter i and j
    if (i >= fDim || i >= fDim)
      return 0;
    if (!fState.HasCovariance())
      return 0;  // no info available when minimization has failed
    if (fState.Parameter(i).IsFixed() || fState.Parameter(i).IsConst())
      return 0;
    if (fState.Parameter(j).IsFixed() || fState.Parameter(j).IsConst())
      return 0;
    unsigned int k = fState.IntOfExt(i);
    unsigned int l = fState.IntOfExt(j);
    double cij = fState.IntCovariance()(k, l);
    double tmp = std::sqrt(std::abs(fState.IntCovariance()(k, k) * fState.IntCovariance()(l, l)));
    if (tmp > 0)
      return cij / tmp;
    return 0;
  }

  double HybridMinimizer::GlobalCC(unsigned int i) const {
    // get global correlation coefficient for the parameter i. This is a number between zero and one which gives
    // the correlation between the i-th parameter  and that linear combination of all other parameters which
    // is most strongly correlated with i.

    if (i >= fDim || i >= fDim)
      return 0;
    // no info available when minimization has failed or has some problems
    if (!fState.HasGlobalCC())
      return 0;
    if (fState.Parameter(i).IsFixed() || fState.Parameter(i).IsConst())
      return 0;
    unsigned int k = fState.IntOfExt(i);
    return fState.GlobalCC().GlobalCC()[k];
  }

  bool HybridMinimizer::GetMinosError(unsigned int i, double &errLow, double &errUp, int runopt) {
    // return the minos error for parameter i
    // if a minimum does not exist an error is returned
    // runopt is a flag which specifies if only lower or upper error needs to be run
    // if runopt = 0 both, = 1 only lower, + 2 only upper errors
    errLow = 0;
    errUp = 0;
    bool runLower = runopt != 2;
    bool runUpper = runopt != 1;

    assert(fMinuitFCN);

    // need to know if parameter is const or fixed
    if (fState.Parameter(i).IsConst() || fState.Parameter(i).IsFixed()) {
      return false;
    }

    int debugLevel = PrintLevel();
    // internal minuit messages
    MnPrint::SetLevel(debugLevel);

    // to run minos I need function minimum class
    // redo minimization from current state
    //    ROOT::Minuit2::FunctionMinimum min =
    //       GetMinimizer()->Minimize(*GetFCN(),fState, ROOT::Minuit2::MnStrategy(strategy), MaxFunctionCalls(), Tolerance());
    //    fState = min.UserState();
    if (fMinimum == nullptr) {
      MN_ERROR_MSG("HybridMinimizer::GetMinosErrors:  failed - no function minimum existing");
      return false;
    }

    if (!fMinimum->IsValid()) {
      MN_ERROR_MSG("HybridMinimizer::MINOS failed due to invalid function minimum");
      return false;
    }

    fMinuitFCN->SetErrorDef(ErrorDef());
    // if error def has been changed update it in FunctionMinimum
    if (ErrorDef() != fMinimum->Up())
      fMinimum->SetErrorDef(ErrorDef());

    // switch off Minuit2 printing
    int prev_level = (PrintLevel() <= 0) ? TurnOffPrintInfoLevel() : -2;

    // set the precision if needed
    if (Precision() > 0)
      fState.SetPrecision(Precision());

    ROOT::Minuit2::MnMinos minos(*fMinuitFCN, *fMinimum);

    // run MnCross
    MnCross low;
    MnCross up;
    int maxfcn = MaxFunctionCalls();
    double tol = Tolerance();

    //   const char * par_name = fState.Name(i);

    // now input tolerance for migrad calls inside Minos (MnFunctionCross)
    // before it was fixed to 0.05
    // cut off too small tolerance (they are not needed)
    tol = std::max(tol, 0.01);

    /*
   if (PrintLevel() >=1) { 
      // print the real number of maxfcn used (defined in MnMinos)
      int maxfcn_used = maxfcn; 
      if (maxfcn_used == 0) { 
    int nvar = fState.VariableParameters();
    maxfcn_used = 2*(nvar+1)*(200 + 100*nvar + 5*nvar*nvar);
      }
//      std::cout << "HybridMinimizer::GetMinosError for parameter " << i << "  " << par_name
//                << " using max-calls " << maxfcn_used << ", tolerance " << tol << std::endl; 
   }
   */

    if (runLower)
      low = minos.Loval(i, maxfcn, tol);
    if (runUpper)
      up = minos.Upval(i, maxfcn, tol);

    ROOT::Minuit2::MinosError me(i, fMinimum->UserState().Value(i), low, up);

    if (prev_level > -2)
      RestoreGlobalPrintLevel(prev_level);

    // debug result of Minos
    // print error message in Minos

    if (debugLevel >= 1) {
      /*
      if (runLower) { 
         if (!me.LowerValid() )  
            std::cout << "Minos:  Invalid lower error for parameter " << par_name << std::endl; 
         if(me.AtLowerLimit()) 
            std::cout << "Minos:  Parameter : " << par_name << "  is at Lower limit."<<std::endl;
         if(me.AtLowerMaxFcn())
            std::cout << "Minos:  Maximum number of function calls exceeded when running for lower error" <<std::endl;   
         if(me.LowerNewMin() )
            std::cout << "Minos:  New Minimum found while running Minos for lower error" <<std::endl;     

         if (debugLevel > 1)  std::cout << "Minos: Lower error for parameter " << par_name << "  :  " << me.Lower() << std::endl; 

      }
      if (runUpper) {          
         if (!me.UpperValid() )  
            std::cout << "Minos:  Invalid upper error for parameter " << par_name << std::endl; 
         if(me.AtUpperLimit()) 
            std::cout << "Minos:  Parameter " << par_name << " is at Upper limit."<<std::endl;
         if(me.AtUpperMaxFcn())
            std::cout << "Minos:  Maximum number of function calls exceeded when running for upper error" <<std::endl;   
         if(me.UpperNewMin() )
            std::cout << "Minos:  New Minimum found while running Minos for upper error" <<std::endl;              

         if (debugLevel > 1)  std::cout << "Minos: Upper error for parameter " << par_name << "  :  " << me.Upper() << std::endl;
      }
*/
    }

    bool lowerInvalid = (runLower && !me.LowerValid());
    bool upperInvalid = (runUpper && !me.UpperValid());
    int mstatus = 0;
    if (lowerInvalid || upperInvalid) {
      // set status accroding to bit
      // bit 1:  lower invalid Minos errors
      // bit 2:  uper invalid Minos error
      // bit 3:   invalid because max FCN
      // bit 4 : invalid because a new minimum has been found
      if (lowerInvalid) {
        mstatus |= 1;
        if (me.AtLowerMaxFcn())
          mstatus |= 4;
        if (me.LowerNewMin())
          mstatus |= 8;
      }
      if (upperInvalid) {
        mstatus |= 3;
        if (me.AtUpperMaxFcn())
          mstatus |= 4;
        if (me.UpperNewMin())
          mstatus |= 8;
      }
      //std::cout << "Error running Minos for parameter " << i << std::endl;
      fStatus += 10 * mstatus;
    }

    errLow = me.Lower();
    errUp = me.Upper();

    bool isValid = (runLower && me.LowerValid()) || (runUpper && me.UpperValid());
    return isValid;
  }

  bool HybridMinimizer::Scan(unsigned int ipar, unsigned int &nstep, double *x, double *y, double xmin, double xmax) {
    // scan a parameter (variable) around the minimum value
    // the parameters must have been set before
    // if xmin=0 && xmax == 0  by default scan around 2 sigma of the error
    // if the errors  are also zero then scan from min and max of parameter range

    if (!fMinuitFCN) {
      MN_ERROR_MSG2("HybridMinimizer::Scan", " Function must be set before using Scan");
      return false;
    }

    if (ipar > fState.MinuitParameters().size()) {
      MN_ERROR_MSG2("HybridMinimizer::Scan", " Invalid number. Minimizer variables must be set before using Scan");
      return false;
    }

    // switch off Minuit2 printing
    int prev_level = (PrintLevel() <= 0) ? TurnOffPrintInfoLevel() : -2;

    MnPrint::SetLevel(PrintLevel());

    // set the precision if needed
    if (Precision() > 0)
      fState.SetPrecision(Precision());

    MnParameterScan scan(*fMinuitFCN, fState.Parameters());
    double amin = scan.Fval();  // fcn value of the function before scan

    // first value is param value
    std::vector<std::pair<double, double> > result = scan(ipar, nstep - 1, xmin, xmax);

    if (prev_level > -2)
      RestoreGlobalPrintLevel(prev_level);

    if (result.size() != nstep) {
      MN_ERROR_MSG2("HybridMinimizer::Scan", " Invalid result from MnParameterScan");
      return false;
    }
    // sort also the returned points in x
    std::sort(result.begin(), result.end());

    for (unsigned int i = 0; i < nstep; ++i) {
      x[i] = result[i].first;
      y[i] = result[i].second;
    }

    // what to do if a new minimum has been found ?
    // use that as new minimum
    if (scan.Fval() < amin) {
      if (PrintLevel() > 0)
        MN_INFO_MSG2("HybridMinimizer::Scan", "A new minimum has been found");
      fState.SetValue(ipar, scan.Parameters().Value(ipar));
    }

    return true;
  }

  bool HybridMinimizer::Contour(unsigned int ipar, unsigned int jpar, unsigned int &npoints, double *x, double *y) {
    // contour plot for parameter i and j
    // need a valid FunctionMinimum otherwise exits
    if (fMinimum == nullptr) {
      MN_ERROR_MSG2("HybridMinimizer::Contour", " no function minimum existing. Must minimize function before");
      return false;
    }

    if (!fMinimum->IsValid()) {
      MN_ERROR_MSG2("HybridMinimizer::Contour", "Invalid function minimum");
      return false;
    }
    assert(fMinuitFCN);

    fMinuitFCN->SetErrorDef(ErrorDef());
    // if error def has been changed update it in FunctionMinimum
    if (ErrorDef() != fMinimum->Up())
      fMinimum->SetErrorDef(ErrorDef());

    // switch off Minuit2 printing (for level of  0,1)
    int prev_level = (PrintLevel() <= 1) ? TurnOffPrintInfoLevel() : -2;

    MnPrint::SetLevel(PrintLevel());

    // set the precision if needed
    if (Precision() > 0)
      fState.SetPrecision(Precision());

    // eventually one should specify tolerance in contours
    MnContours contour(*fMinuitFCN, *fMinimum, Strategy());

    if (prev_level > -2)
      RestoreGlobalPrintLevel(prev_level);

    std::vector<std::pair<double, double> > result = contour(ipar, jpar, npoints);
    if (result.size() != npoints) {
      MN_ERROR_MSG2("HybridMinimizer::Contour", " Invalid result from MnContours");
      return false;
    }
    for (unsigned int i = 0; i < npoints; ++i) {
      x[i] = result[i].first;
      y[i] = result[i].second;
    }

    return true;
  }

  bool HybridMinimizer::Hesse() {
    // find Hessian (full second derivative calculations)
    // the contained state will be updated with the Hessian result
    // in case a function minimum exists and is valid the result will be
    // appended in the function minimum

    if (!fMinuitFCN) {
      MN_ERROR_MSG2("HybridMinimizer::Hesse", "FCN function has not been set");
      return false;
    }

    int strategy = Strategy();
    int maxfcn = MaxFunctionCalls();

    // switch off Minuit2 printing
    int prev_level = (PrintLevel() <= 0) ? TurnOffPrintInfoLevel() : -2;

    MnPrint::SetLevel(PrintLevel());

    // set the precision if needed
    if (Precision() > 0)
      fState.SetPrecision(Precision());

    ROOT::Minuit2::MnHesse hesse(strategy);

    // case when function minimum exists
    if (fMinimum) {
      // run hesse and function minimum will be updated with Hesse result
      hesse(*fMinuitFCN, *fMinimum, maxfcn);
      fState = fMinimum->UserState();
    }

    else {
      // run Hesse on point stored in current state (independent of function minimum validity)
      // (x == 0)
      fState = hesse(*fMinuitFCN, fState, maxfcn);
    }

    if (prev_level > -2)
      RestoreGlobalPrintLevel(prev_level);

    if (PrintLevel() >= 3) {
      //      std::cout << "State returned from Hesse " << std::endl;
      //      std::cout << fState << std::endl;
    }

    if (!fState.HasCovariance()) {
      // if false means error is not valid and this is due to a failure in Hesse
      if (PrintLevel() > 0)
        MN_INFO_MSG2("HybridMinimizer::Hesse", "Hesse failed ");
      // update minimizer error status
      int hstatus = 4;
      // information on error state can be retrieved only if fMinimum is available
      if (fMinimum) {
        if (fMinimum->Error().HesseFailed())
          hstatus = 1;
        if (fMinimum->Error().InvertFailed())
          hstatus = 2;
        else if (!(fMinimum->Error().IsPosDef()))
          hstatus = 3;
      }
      fStatus += 100 * hstatus;
      return false;
    }

    return true;
  }

  int HybridMinimizer::CovMatrixStatus() const {
    // return status of covariance matrix
    //-1 - not available (inversion failed or Hesse failed)
    // 0 - available but not positive defined
    // 1 - covariance only approximate
    // 2 full matrix but forced pos def
    // 3 full accurate matrix

    if (fMinimum) {
      // case a function minimum  is available
      if (fMinimum->HasAccurateCovar())
        return 3;
      else if (fMinimum->HasMadePosDefCovar())
        return 2;
      else if (fMinimum->HasValidCovariance())
        return 1;
      else if (fMinimum->HasCovariance())
        return 0;
      return -1;
    } else {
      // case fMinimum is not available - use state information
      return fState.CovarianceStatus();
    }
    return 0;
  }

}  // namespace PSFitter