TKDE.cxx

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// // @(#)root/hist:$Id$
// Authors: Bartolomeu Rabacal    07/2010
/**********************************************************************
 *                                                                    *
 * Copyright (c) 2006 , ROOT MathLib Team                             *
 *                                                                    *
 * For the licensing terms see $ROOTSYS/LICENSE.                      *
 * For the list of contributors see $ROOTSYS/README/CREDITS.          *
 *                                                                    *
 **********************************************************************/
//////////////////////////////////////////////////////////////////////////////
/** \class TKDE
    \ingroup Hist
 Kernel Density Estimation class.
 The three main references are:
 1. "Scott DW, Multivariate Density Estimation. Theory, Practice and Visualization. New York: Wiley",
 2. "Jann Ben - ETH Zurich, Switzerland -, Univariate kernel density estimation document for KDENS:
    Stata module for univariate kernel density estimation."
 3. "Hardle W, Muller M, Sperlich S, Werwatz A, Nonparametric and Semiparametric Models. Springer."
 4. "Cranmer KS, Kernel Estimation in High-Energy
 Physics. Computer Physics Communications 136:198-207,2001" - e-Print Archive: hep ex/0011057.
 
 The algorithm is briefly described in (4). A binned version is also implemented to address the 
 performance issue due to its data size dependance.
 */


#include <functional>
#include <algorithm>
#include <numeric>
#include <limits>
#include <cassert>

#include "Math/Error.h"
#include "TMath.h"
#include "Math/Functor.h"
#include "Math/Integrator.h"
#include "Math/QuantFuncMathCore.h"
#include "Math/RichardsonDerivator.h"
#include "TGraphErrors.h"
#include "TF1.h"
#include "TH1.h"
#include "TCanvas.h"
#include "TKDE.h"


ClassImp(TKDE);

class TKDE::TKernel {
   TKDE* fKDE;
   UInt_t fNWeights; // Number of kernel weights (bandwidth as vectorized for binning)
   std::vector<Double_t> fWeights; // Kernel weights (bandwidth)
public:
   TKernel(Double_t weight, TKDE* kde);
   void ComputeAdaptiveWeights();
   Double_t operator()(Double_t x) const;
   Double_t GetWeight(Double_t x) const;
   Double_t GetFixedWeight() const;
   const std::vector<Double_t> & GetAdaptiveWeights() const;
};

struct TKDE::KernelIntegrand {
   enum EIntegralResult{kNorm, kMu, kSigma2, kUnitIntegration};
   KernelIntegrand(const TKDE* kde, EIntegralResult intRes);
   Double_t operator()(Double_t x) const;
private:
   const TKDE* fKDE;
   EIntegralResult fIntegralResult;
};

/// default constructor used by I/O
TKDE::TKDE() :
   fKernelFunction(nullptr),
   fKernel(nullptr),
   fPDF(nullptr),
   fUpperPDF(nullptr),
   fLowerPDF(nullptr),
   fApproximateBias(nullptr),
   fGraph(nullptr),
   fUseMirroring(false), fMirrorLeft(false), fMirrorRight(false), fAsymLeft(false), fAsymRight(false),
   fUseBins(false), fNewData(false), fUseMinMaxFromData(false),
   fNBins(0), fNEvents(0), fSumOfCounts(0), fUseBinsNEvents(0),
   fMean(0.),fSigma(0.), fSigmaRob(0.), fXMin(0.), fXMax(0.),
   fRho(0.), fAdaptiveBandwidthFactor(0.), fWeightSize(0)
{
}

TKDE::~TKDE() {
   //Class destructor
   if (fPDF)              delete fPDF;
   if (fUpperPDF)         delete fUpperPDF;
   if (fLowerPDF)         delete fLowerPDF;
   if (fGraph)         delete fGraph;
   if (fApproximateBias)  delete fApproximateBias;
   if (fKernelFunction && fKernelType != kUserDefined) delete fKernelFunction;
   if (fKernel) delete fKernel;
}

void TKDE::Instantiate(KernelFunction_Ptr kernfunc, UInt_t events, const Double_t* data, const Double_t* dataWeights, Double_t xMin, Double_t xMax, const Option_t* option, Double_t rho) {
   // Template's constructor surrogate

   fData = std::vector<Double_t>(events, 0.0);
   fEvents = std::vector<Double_t>(events, 0.0);
   fPDF = 0;
   fKernel = 0;
   fKernelFunction = 0;
   fUpperPDF = 0;
   fLowerPDF = 0;
   fApproximateBias = 0;
   fGraph = 0;
   fNewData = false;
   fUseMirroring = false; fMirrorLeft = false; fMirrorRight = false;
   fAsymLeft = false; fAsymRight = false; 
   fNBins = events < 10000 ? 100 : events / 10;
   fNEvents = events;
   fUseBinsNEvents = 10000;
   fMean = 0.0;
   fSigma = 0.0;
   fXMin = xMin;
   fXMax = xMax;
   fUseMinMaxFromData = (fXMin >= fXMax);
   fSumOfCounts = 0;
   fAdaptiveBandwidthFactor = 1.;
   fRho = rho;
   fWeightSize = 0;
   fCanonicalBandwidths = std::vector<Double_t>(kTotalKernels, 0.0);
   fKernelSigmas2 = std::vector<Double_t>(kTotalKernels, -1.0);
   fSettedOptions = std::vector<Bool_t>(4, kFALSE);
   SetOptions(option, rho);
   CheckOptions(kTRUE);
   SetMirror();
   SetUseBins();
   SetData(data, dataWeights);
   SetKernelFunction(kernfunc);

}

void TKDE::SetOptions(const Option_t* option, Double_t rho) {
   //Sets User defined construction options
   TString opt = option;
   opt.ToLower();
   std::string options = opt.Data();
   size_t numOpt = 4;
   std::vector<std::string> voption(numOpt, "");
   for (std::vector<std::string>::iterator it = voption.begin(); it != voption.end() && !options.empty(); ++it) {
      size_t pos = options.find_last_of(';');
      if (pos == std::string::npos) {
         *it = options;
         break;
      }
      *it = options.substr(pos + 1);
      options = options.substr(0, pos);
   }
   for (std::vector<std::string>::iterator it = voption.begin(); it != voption.end(); ++it) {
      size_t pos = (*it).find(':');
      if (pos != std::string::npos) {
         GetOptions((*it).substr(0, pos) , (*it).substr(pos + 1));
      }
   }
   AssureOptions();
   fRho = rho;
}

void TKDE::SetDrawOptions(const Option_t* option, TString& plotOpt, TString& drawOpt) {
   // Sets User defined drawing options
   size_t numOpt = 2;
   std::string options = TString(option).Data();
   std::vector<std::string> voption(numOpt, "");
   for (std::vector<std::string>::iterator it = voption.begin(); it != voption.end() && !options.empty(); ++it) {
      size_t pos = options.find_last_of(';');
      if (pos == std::string::npos) {
         *it = options;
         break;
      }
      *it = options.substr(pos + 1);
      options = options.substr(0, pos);
   }
   Bool_t foundPlotOPt = kFALSE;
   Bool_t foundDrawOPt = kFALSE;
   for (std::vector<std::string>::iterator it = voption.begin(); it != voption.end() && !options.empty(); ++it) {
      size_t pos = (*it).find(':');
      if (pos == std::string::npos) break;
      TString optionType = (*it).substr(0, pos);
      TString optionInstance = (*it).substr(pos + 1);
      optionType.ToLower();
      optionInstance.ToLower();
      if (optionType.Contains("plot")) {
         foundPlotOPt = kTRUE;
         if (optionInstance.Contains("estimate") || optionInstance.Contains("errors") || optionInstance.Contains("confidenceinterval"))
            plotOpt = optionInstance;
         else
            this->Warning("SetDrawOptions", "Unknown plotting option: setting to KDE estimate plot.");
      } else if (optionType.Contains("drawoptions")) {
         foundDrawOPt = kTRUE;
         drawOpt = optionInstance;
      }
   }
   if (!foundPlotOPt) {
      this->Warning("SetDrawOptions", "No plotting option: setting to KDE estimate plot.");
      plotOpt = "estimate";
   }
   if (!foundDrawOPt) {
      this->Warning("SetDrawOptions", "No drawing options: setting to default ones.");
      drawOpt = "apl4";
   }
}

void TKDE::GetOptions(std::string optionType, std::string option) {
   // Gets User defined KDE construction options
   if (optionType.compare("kerneltype") == 0) {
      fSettedOptions[0] = kTRUE;
      if (option.compare("gaussian") == 0) {
         fKernelType = kGaussian;
      } else if (option.compare("epanechnikov") == 0) {
         fKernelType = kEpanechnikov;
      } else if (option.compare("biweight") == 0) {
         fKernelType = kBiweight;
      } else if (option.compare("cosinearch") == 0) {
         fKernelType = kCosineArch;
      } else if (option.compare("userdefined") == 0) {
         fKernelType = kUserDefined;
      } else {
         this->Warning("GetOptions", "Unknown kernel type option: setting to Gaussian");
         fKernelType = kGaussian;
      }
   } else if (optionType.compare("iteration") == 0) {
      fSettedOptions[1] = kTRUE;
      if (option.compare("adaptive") == 0) {
         fIteration = kAdaptive;
      } else if (option.compare("fixed") == 0) {
         fIteration = kFixed;
      } else {
         this->Warning("GetOptions", "Unknown iteration option: setting to Adaptive");
         fIteration = kAdaptive;
      }
   } else if (optionType.compare("mirror") == 0) {
      fSettedOptions[2] = kTRUE;
      if (option.compare("nomirror") == 0) {
         fMirror = kNoMirror;
      } else if (option.compare("mirrorleft") == 0) {
         fMirror = kMirrorLeft;
      } else if (option.compare("mirrorright") == 0) {
         fMirror = kMirrorRight;
      } else if (option.compare("mirrorboth") == 0) {
         fMirror = kMirrorBoth;
      } else if (option.compare("mirrorasymleft") == 0) {
         fMirror = kMirrorAsymLeft;
      } else if (option.compare("mirrorasymleftright") == 0) {
         fMirror = kMirrorAsymLeftRight;
      } else if (option.compare("mirrorasymright") == 0) {
         fMirror = kMirrorAsymRight;
      } else if (option.compare("mirrorleftasymright") == 0) {
         fMirror = kMirrorLeftAsymRight;
      } else if (option.compare("mirrorasymboth") == 0) {
         fMirror = kMirrorAsymBoth;
      } else {
         this->Warning("GetOptions", "Unknown mirror option: setting to NoMirror");
         fMirror = kNoMirror;
      }
   } else if (optionType.compare("binning") == 0) {
      fSettedOptions[3] = kTRUE;
      if (option.compare("unbinned") == 0) {
         fBinning = kUnbinned;
      } else if (option.compare("relaxedbinning") == 0) {
         fBinning = kRelaxedBinning;
      } else if (option.compare("forcedbinning") == 0) {
         fBinning = kForcedBinning;
      } else {
         this->Warning("GetOptions", "Unknown binning option: setting to RelaxedBinning");
         fBinning = kRelaxedBinning;
      }
   }
}

void TKDE::AssureOptions() {
   // Sets missing construction options to default ones
   if (!fSettedOptions[0]) {
      fKernelType = kGaussian;
   }
   if (!fSettedOptions[1]) {
      fIteration = kAdaptive;
   }
   if (!fSettedOptions[2]) {
      fMirror = kNoMirror;
   }
   if (!fSettedOptions[3]) {
      fBinning = kRelaxedBinning;
   }
}

void TKDE::CheckOptions(Bool_t isUserDefinedKernel) {
   // Sets User global options
   if (!(isUserDefinedKernel) && !(fKernelType >= kGaussian && fKernelType < kUserDefined)) {
      Error("CheckOptions", "Illegal user kernel type input! Use template constructor for user defined kernel.");
   }
   if (fIteration != kAdaptive && fIteration != kFixed) {
      Warning("CheckOptions", "Illegal user iteration type input - use default value !");
      fIteration = kAdaptive;
   }
   if (!(fMirror >= kNoMirror && fMirror <= kMirrorAsymBoth)) {
      Warning("CheckOptions", "Illegal user mirroring type input - use default value !");
      fMirror = kNoMirror;
   }
   if (!(fBinning >= kUnbinned && fBinning <= kForcedBinning)) {
      Warning("CheckOptions", "Illegal user binning type input - use default value !");
      fBinning = kRelaxedBinning;
   }
   if (fRho <= 0.0) {
      Warning("CheckOptions", "Tuning factor rho cannot be non-positive - use default value !");
      fRho = 1.0;
   }
}

void TKDE::SetKernelType(EKernelType kern) {
   // Sets User option for the choice of kernel estimator
   if (fKernelFunction && fKernelType != kUserDefined) {
      delete fKernelFunction;
      fKernelFunction = 0;
   }
   fKernelType = kern;
   CheckOptions();
   SetKernelFunction(0);
}

void TKDE::SetIteration(EIteration iter) {
   // Sets User option for fixed or adaptive iteration
   fIteration = iter;
   CheckOptions();
   SetKernel();
}


void TKDE::SetMirror(EMirror mir) {
   // Sets User option for mirroring the data
   fMirror = mir;
   CheckOptions();
   SetMirror();
   if (fUseMirroring) {
      SetMirroredEvents();
   }
   SetKernel();
}


void TKDE::SetBinning(EBinning bin) {
   // Sets User option for binning the weights
   fBinning = bin;
   CheckOptions();
   SetUseBins();
}

void TKDE::SetNBins(UInt_t nbins) {
   // Sets User option for number of bins
   if (!nbins) {
      Error("SetNBins", "Number of bins must be greater than zero.");
      return;
   }

   fNBins = nbins;
   fWeightSize = fNBins / (fXMax - fXMin);

   SetUseBins();
   if (!fUseBins) {
      if (fBinning == kUnbinned) 
         Warning("SetNBins", "Bin type using SetBinning must be set for using a binned evaluation");
      else 
         Warning("SetNBins", "Bin type using SetBinning or with SetUseBinsNEvents must be set for using a binned evaluation");
   }
}

void TKDE::SetUseBinsNEvents(UInt_t nEvents) {
   // Sets User option for the minimum number of events for allowing automatic binning
   fUseBinsNEvents = nEvents;
   SetUseBins();
}

void TKDE::SetTuneFactor(Double_t rho) {
   // Factor which can be used to tune the smoothing.
   // It is used as multiplicative factor for the fixed and adaptive bandwidth.
   // A value < 1 will reproduce better the tails but oversmooth the peak
   // while a factor > 1 will overestimate the tail
   fRho = rho;
   CheckOptions();
   SetKernel();
}

void TKDE::SetRange(Double_t xMin, Double_t xMax) {
   // Sets minimum range value and maximum range value
   if (xMin >= xMax) {
      Error("SetRange", "Minimum range cannot be bigger or equal than the maximum range! Present range values remain the same.");
      return;
   }
   fXMin = xMin;
   fXMax = xMax;
   fUseMinMaxFromData = false;
   SetKernel();
}

// private methods

void TKDE::SetUseBins() {
   // Sets User option for using binned weights
   switch (fBinning) {
      default:
      case kRelaxedBinning:
         if (fNEvents >= fUseBinsNEvents) {
            fUseBins = kTRUE;
         } else {
            fUseBins = kFALSE;
         }
         break;
      case kForcedBinning:
         fUseBins = kTRUE;
         break;
      case kUnbinned:
         fUseBins = kFALSE;
   }

   // set the binning
   if (fUseBins &&  !fEvents.empty() ) {
      SetBinCentreData(fXMin, fXMax);
      SetBinCountData();
      SetKernel();
   }
}

void TKDE::SetMirror() {
   // Sets the mirroring
   fMirrorLeft   = fMirror == kMirrorLeft      || fMirror == kMirrorBoth          || fMirror == kMirrorLeftAsymRight;
   fMirrorRight  = fMirror == kMirrorRight     || fMirror == kMirrorBoth          || fMirror == kMirrorAsymLeftRight;
   fAsymLeft     = fMirror == kMirrorAsymLeft  || fMirror == kMirrorAsymLeftRight || fMirror == kMirrorAsymBoth;
   fAsymRight    = fMirror == kMirrorAsymRight || fMirror == kMirrorLeftAsymRight || fMirror == kMirrorAsymBoth;
   fUseMirroring = fMirrorLeft                 || fMirrorRight ;
}

void TKDE::SetData(const Double_t* data, const Double_t* wgts) {
   // Sets the data events input sample or bin centres for binned option and computes basic estimators
   if (!data) {
      if (fNEvents) fData.reserve(fNEvents);
      return;
   }
   fEvents.assign(data, data + fNEvents);
   if (wgts) fEventWeights.assign(wgts, wgts + fNEvents);
   
   if (fUseMinMaxFromData) {
      fXMin = *std::min_element(fEvents.begin(), fEvents.end());
      fXMax = *std::max_element(fEvents.begin(), fEvents.end());
   }

   if (fUseBins) {
      if (fNBins >= fNEvents) {
         this->Warning("SetData", "Default number of bins is greater or equal to number of events. Use SetNBins(UInt_t) to set the appropriate number of bins");
      }
      fWeightSize = fNBins / (fXMax - fXMin);
      SetBinCentreData(fXMin, fXMax);
   } else {
      fWeightSize = fNEvents / (fXMax - fXMin);
      fData = fEvents;
   }
   // to set fBinCount and fSumOfCounts
   SetBinCountData();


   ComputeDataStats(); 
   if (fUseMirroring) {
      SetMirroredEvents();
   }
}

void TKDE::ReInit() {
   // re-initialize the KDE in case of new data or in case of reading from a file

   // in case of new data re-compute the statistics (works only for unbinned case)
   if (fNewData)  {
      InitFromNewData();
      return;
   }
   // case of reading from a file.
   // we need to recreate Kernel class (with adaptive weights if needed) and
   // recreate kernel function pointer

   if (fKernelFunction) Error("ReInit","Kernel function pointer should be a nullptr when re-initializing after reading from a file");

   if (fEvents.size() == 0) {
      Error("ReInit","TKDE does not contain any data !");
      return;
   }
       
   SetKernelFunction(0);

   SetKernel();
}

void TKDE::InitFromNewData() {
   // re-initialize when new data have been filled in TKDE
   // re-compute kernel quantities and statistics
   if (fUseBins) {
      Error("InitFromNewData","Re-felling is not supported with binning");
      return;
   }

   fNewData = false;
   // in case of unbinned data
   if (!fUseBins) fEvents = fData;
   if (fUseMinMaxFromData) {
      fXMin = *std::min_element(fEvents.begin(), fEvents.end());
      fXMax = *std::max_element(fEvents.begin(), fEvents.end());
   }
   ComputeDataStats(); 
   //    if (fUseBins) {
   // } // bin usage is not supported in this case
   //
   fWeightSize = fNEvents / (fXMax - fXMin);
   if (fUseMirroring) {
      SetMirroredEvents();
   }
   // in case of I/O reset the kernel
}

void TKDE::SetMirroredEvents() {
   // Mirrors the data 
   std::vector<Double_t> originalEvents = fEvents;
   std::vector<Double_t> originalWeights = fEventWeights;
  if (fMirrorLeft) {
      fEvents.resize(2 * fNEvents, 0.0);
      transform(fEvents.begin(), fEvents.begin() + fNEvents, fEvents.begin() + fNEvents,
                std::bind(std::minus<Double_t>(), 2 * fXMin, std::placeholders::_1));
   }
   if (fMirrorRight) {
      fEvents.resize((fMirrorLeft + 2) * fNEvents, 0.0);
      transform(fEvents.begin(), fEvents.begin() + fNEvents, fEvents.begin() + (fMirrorLeft + 1) * fNEvents,
                std::bind(std::minus<Double_t>(), 2 * fXMax, std::placeholders::_1));
   }
   if (!fEventWeights.empty() && (fMirrorLeft || fMirrorRight)) {
      // copy weights too
      fEventWeights.insert(fEventWeights.end(), fEventWeights.begin(), fEventWeights.end() ); 
   }

   if(fUseBins) {
      fNBins *= (fMirrorLeft + fMirrorRight + 1);
      Double_t xmin = fMirrorLeft  ? 2 * fXMin - fXMax : fXMin;
      Double_t xmax = fMirrorRight ? 2 * fXMax - fXMin : fXMax;
      SetBinCentreData(xmin, xmax);
   } else {
      fData = fEvents;
   }
   SetBinCountData();
   
   fEvents = originalEvents;
   fEventWeights = originalWeights; 
}

void TKDE::SetMean() {
   // Computes input data's mean
   fMean = std::accumulate(fEvents.begin(), fEvents.end(), 0.0) / fEvents.size();
}

void TKDE::SetSigma(Double_t R) {
   // Computes input data's sigma
   fSigma = std::sqrt(1. / (fEvents.size() - 1.) * (std::inner_product(fEvents.begin(), fEvents.end(), fEvents.begin(), 0.0) - fEvents.size() * std::pow(fMean, 2.)));
   fSigmaRob = std::min(fSigma, R / 1.349); // Sigma's robust estimator
}

void TKDE::SetKernel() {
   // Sets the kernel density estimator
   UInt_t n = fData.size();
   if (n == 0) return;
   // Optimal bandwidth (Silverman's rule of thumb with assumed Gaussian density)
   Double_t weight = fCanonicalBandwidths[kGaussian] * fSigmaRob * std::pow(3. / (8. * std::sqrt(M_PI)) * n, -0.2);
   weight *= fRho * fCanonicalBandwidths[fKernelType] / fCanonicalBandwidths[kGaussian];
   if (fKernel) delete fKernel;
   fKernel = new TKernel(weight, this);
   if (fIteration == kAdaptive) {
      fKernel->ComputeAdaptiveWeights();
   }
   //std::cout << "setting the kernel - n = " << n << " weight is " << weight << "  " << fRho << "  " << fSigmaRob << "   " << fSigma << "   " << fMean << "  " << fCanonicalBandwidths[kGaussian] <<  std::endl;
}

void TKDE::SetKernelFunction(KernelFunction_Ptr kernfunc) {

   assert(fKernelFunction == 0);  // to avoid memory leaks
   switch (fKernelType) {
      case kGaussian :
         fKernelFunction = new ROOT::Math::WrappedMemFunction<TKDE, Double_t (TKDE::*)(Double_t) const>(*this, &TKDE::GaussianKernel);
         break;
      case kEpanechnikov :
         fKernelFunction = new ROOT::Math::WrappedMemFunction<TKDE, Double_t (TKDE::*)(Double_t) const>(*this, &TKDE::EpanechnikovKernel);
         break;
      case kBiweight :
         fKernelFunction = new ROOT::Math::WrappedMemFunction<TKDE, Double_t (TKDE::*)(Double_t) const>(*this, &TKDE::BiweightKernel);
         break;
      case kCosineArch :
         fKernelFunction = new ROOT::Math::WrappedMemFunction<TKDE, Double_t (TKDE::*)(Double_t) const>(*this, &TKDE::CosineArchKernel);
         break;
      case kUserDefined :
         fKernelFunction = kernfunc;
         if (fKernelFunction)  CheckKernelValidity();
         break;
      case kTotalKernels :
      default:
         /// for user defined kernels
         fKernelFunction = kernfunc;
         fKernelType = kUserDefined; 
   }

   if (fKernelType == kUserDefined) { 
      if (fKernelFunction) {
         CheckKernelValidity();
         SetUserCanonicalBandwidth();
         SetUserKernelSigma2();
      }
      else {
         Error("SetKernelFunction", "User kernel function is not defined !");
         return;
      }
   }
   assert(fKernelFunction); 
   SetKernelSigmas2();
   SetCanonicalBandwidths();
   SetKernel();
}

void TKDE::SetCanonicalBandwidths() {
   // Sets the canonical bandwidths according to the kernel type
   fCanonicalBandwidths[kGaussian] = 0.7764;     // Checked in Mathematica
   fCanonicalBandwidths[kEpanechnikov] = 1.7188; // Checked in Mathematica
   fCanonicalBandwidths[kBiweight] = 2.03617;    // Checked in Mathematica
   fCanonicalBandwidths[kCosineArch] = 1.7663;   // Checked in Mathematica
   fCanonicalBandwidths[kUserDefined] = 1.0;     // To be Checked 
}

void TKDE::SetKernelSigmas2() {
   // Sets the kernel sigmas2 according to the kernel type
   fKernelSigmas2[kGaussian] = 1.0;
   fKernelSigmas2[kEpanechnikov] = 1.0 / 5.0;
   fKernelSigmas2[kBiweight] = 1.0 / 7.0;
   fKernelSigmas2[kCosineArch] = 1.0 - 8.0 / std::pow(M_PI, 2);
}

TF1* TKDE::GetFunction(UInt_t npx, Double_t xMin, Double_t xMax) {
   // Returns the PDF estimate as a function sampled in npx between xMin and xMax
   // the KDE is not re-normalized to the xMin/xMax range.
   // The user manages the returned function
   // For getting a non-sampled TF1, one can create a TF1 directly from the TKDE by doing
   // TF1 * f1  = new TF1("f1",kde,xMin,xMax,0);
   return GetKDEFunction(npx,xMin,xMax);
}

TF1* TKDE::GetUpperFunction(Double_t confidenceLevel, UInt_t npx, Double_t xMin, Double_t xMax) {
   // Returns the PDF upper estimate (upper confidence interval limit)
   return GetPDFUpperConfidenceInterval(confidenceLevel,npx,xMin,xMax);
}

TF1* TKDE::GetLowerFunction(Double_t confidenceLevel, UInt_t npx, Double_t xMin, Double_t xMax) {
   // Returns the PDF lower estimate (lower confidence interval limit)
   return GetPDFLowerConfidenceInterval(confidenceLevel,npx,xMin,xMax);
}

TF1* TKDE::GetApproximateBias(UInt_t npx, Double_t xMin, Double_t xMax) {
   // Returns the PDF estimate bias
   return GetKDEApproximateBias(npx,xMin,xMax);
}

void TKDE::Fill(Double_t data) {
   // Fills data member with User input data event for the unbinned option
   if (fUseBins) {
      this->Warning("Fill", "Cannot fill data with data binned option. Data input ignored.");
      return;
   }
   fData.push_back(data);
   fNEvents++;
   fNewData = kTRUE;
}

void TKDE::Fill(Double_t data, Double_t weight) {
   // Fills data member with User input data event for the unbinned option
   if (fUseBins) {
      this->Warning("Fill", "Cannot fill data with data binned option. Data input ignored.");
      return;
   }
   fData.push_back(data);  // should not be here fEvent ??
   fEventWeights.push_back(weight);
   fNEvents++;
   fNewData = kTRUE;
}

Double_t TKDE::operator()(const Double_t* x, const Double_t*) const {
   // The class's unary function: returns the kernel density estimate
   return (*this)(*x);
}

Double_t TKDE::operator()(Double_t x) const {
   // The class's unary function: returns the kernel density estimate
   if (!fKernel) {
      (const_cast<TKDE*>(this))->ReInit();
      // in case of failed re-initialization
      if (!fKernel) return TMath::QuietNaN();
   }
   return (*fKernel)(x);
}

Double_t TKDE::GetMean() const {
   // return the mean of the data
   if (fNewData) (const_cast<TKDE*>(this))->InitFromNewData();
   return fMean;
}

Double_t TKDE::GetSigma() const {
   // return the standard deviation  of the data
   if (fNewData) (const_cast<TKDE*>(this))->InitFromNewData();
   return fSigma;
}

Double_t TKDE::GetRAMISE() const {
   // Returns the Root Asymptotic Mean Integrated Squared Error according to Silverman's rule of thumb with assumed Gaussian density
   Double_t result = 5. / 4. * fKernelSigmas2[fKernelType] * std::pow(fCanonicalBandwidths[fKernelType], 4) * std::pow(3. / (8. * std::sqrt(M_PI)) , -0.2) * fSigmaRob * std::pow(fNEvents, -0.8);
   return std::sqrt(result);
}

TKDE::TKernel::TKernel(Double_t weight, TKDE* kde) :
// Internal class constructor
fKDE(kde),
fNWeights(kde->fData.size()),
fWeights(fNWeights, weight)
{}

void TKDE::TKernel::ComputeAdaptiveWeights() {
   // Gets the adaptive weights (bandwidths) for TKernel internal computation
   std::vector<Double_t> weights = fWeights;
   Double_t minWeight = weights[0] * 0.05;
   unsigned int n = fKDE->fData.size();
   assert( n == weights.size() );
   bool useDataWeights = (fKDE->fBinCount.size() == n); 
   Double_t f = 0.0;
   for (unsigned int i = 0; i < n; ++i) { 
//   for (; weight != weights.end(); ++weight, ++data, ++dataW) {
      if (useDataWeights && fKDE->fBinCount[i] <= 0) continue;  // skip negative or null weights
      f = (*fKDE->fKernel)(fKDE->fData[i]);
      if (f <= 0)
         fKDE->Warning("ComputeAdativeWeights","function value is zero or negative for x = %f w = %f",
                       fKDE->fData[i],(useDataWeights) ? fKDE->fBinCount[i] : 1.);
      weights[i] = std::max(weights[i] /= std::sqrt(f), minWeight);
      fKDE->fAdaptiveBandwidthFactor += std::log(f);
      //printf("(f = %f w = %f af = %f ),",f,*weight,fKDE->fAdaptiveBandwidthFactor);
   }
   Double_t kAPPROX_GEO_MEAN = 0.241970724519143365; // 1 / TMath::Power(2 * TMath::Pi(), .5) * TMath::Exp(-.5). Approximated geometric mean over pointwise data (the KDE function is substituted by the "real Gaussian" pdf) and proportional to sigma. Used directly when the mirroring is enabled, otherwise computed from the data
   fKDE->fAdaptiveBandwidthFactor = fKDE->fUseMirroring ? kAPPROX_GEO_MEAN / fKDE->fSigmaRob : std::sqrt(std::exp(fKDE->fAdaptiveBandwidthFactor / fKDE->fData.size()));
   transform(weights.begin(), weights.end(), fWeights.begin(),
             std::bind(std::multiplies<Double_t>(), std::placeholders::_1, fKDE->fAdaptiveBandwidthFactor));
   //printf("adaptive bandwidth factor % f weight 0 %f , %f \n",fKDE->fAdaptiveBandwidthFactor, weights[0],fWeights[0] );
}

Double_t TKDE::TKernel::GetWeight(Double_t x) const {
   // Returns the bandwidth
   return fWeights[fKDE->Index(x)];
}

void TKDE::SetBinCentreData(Double_t xmin, Double_t xmax) {
   // Returns the bins' centres from the data for using with the binned option
   fData.assign(fNBins, 0.0);
   Double_t binWidth((xmax - xmin) / fNBins);
   for (UInt_t i = 0; i < fNBins; ++i) {
      fData[i] = xmin + (i + 0.5) * binWidth;
   }
}

void TKDE::SetBinCountData() {
   // Returns the bins' count from the data for using with the binned option
   // or set the bin count to the weights in case of weighted data
   if (fUseBins) { 
      fBinCount.resize(fNBins);
      fSumOfCounts = 0;
      // case of weighted events 
      if (!fEventWeights.empty() ) { 
         for (UInt_t i = 0; i < fNEvents; ++i) {
            if (fEvents[i] >= fXMin && fEvents[i] < fXMax) {
               fBinCount[Index(fEvents[i])] += fEventWeights[i];
               fSumOfCounts += fEventWeights[i];
               //printf("sum of counts %f - bin count %d - %f \n",fSumOfCounts, Index(fEvents[i]), fBinCount[Index(fEvents[i])] );
            }
         }
      }
      // case of unweighted data 
      else {
         for (UInt_t i = 0; i < fNEvents; ++i) {
            if (fEvents[i] >= fXMin && fEvents[i] < fXMax) {
               fBinCount[Index(fEvents[i])] += 1;
               fSumOfCounts += 1;
            }
         }
      }
   }
   else if (!fEventWeights.empty() ) {
      fBinCount = fEventWeights;
      fSumOfCounts = 0;
      for (UInt_t i = 0; i < fNEvents; ++i) 
         fSumOfCounts += fEventWeights[i];
   }
   else {
      fSumOfCounts = fNEvents;
      fBinCount.clear(); 
   }
}

void TKDE::Draw(const Option_t* opt) {
   // Draws either the KDE functions or its errors
   // Possible options:
   //                    ""  (default) - draw just the kde
   //                    "same" draw on top of existing pad
   //                    "Errors" draw a TGraphErrors with the point and errors
   //                    "confidenceinterval" draw KDE + conf interval functions (default is 95%)
   //                    "confidenceinterval@0.90" draw KDE + conf interval functions at 90%
   //                      Extra options can be passed in opt for drawing the TF1 or the TGraph
   //
   //NOTE:  The functions GetDrawnFunction(), GetDrawnUpperFunction(), GetDrawnLowerFunction()
   //  and GetGraphWithErrors() return the corresponding drawn objects (which are maneged by the TKDE)
   // They can be used to changes style, color, etc...

   // TString plotOpt = "";
   // TString drawOpt = "";
   // LM : this is too complicates - skip it - not needed for just
   // three options
   // SetDrawOptions(opt, plotOpt, drawOpt);
   TString plotOpt = opt;
   plotOpt.ToLower();
   TString drawOpt = plotOpt;
   if(gPad && !plotOpt.Contains("same")) {
      gPad->Clear();
   }
   if (plotOpt.Contains("errors"))  {
      drawOpt.ReplaceAll("errors","");
      DrawErrors(drawOpt);
   }
   else if (plotOpt.Contains("confidenceinterval") ||
            plotOpt.Contains("confinterval")) {
      // parse level option
      drawOpt.ReplaceAll("confidenceinterval","");
      drawOpt.ReplaceAll("confinterval","");
      Double_t level = 0.95;
      const char * s = strstr(plotOpt.Data(),"interval@");
      // coverity [secure_coding : FALSE]
      if (s != 0) sscanf(s,"interval@%lf",&level);
      if((level <= 0) || (level >= 1)) {
         Warning("Draw","given confidence level %.3lf is invalid - use default 0.95",level);
         level = 0.95;
      }
      DrawConfidenceInterval(drawOpt,level);
   }
   else {
      if (fPDF) delete fPDF;
      fPDF = GetKDEFunction();
      fPDF->Draw(drawOpt);
   }
}

void TKDE::DrawErrors(TString& drawOpt) {
   // Draws a TGraphErrors for the KDE errors
   if (fGraph) delete fGraph;
   fGraph = GetGraphWithErrors();
   fGraph->Draw(drawOpt.Data());
}

TGraphErrors* TKDE::GetGraphWithErrors(UInt_t npx, double xmin, double xmax) {
   if (xmin>= xmax) { xmin = fXMin; xmax = fXMax; }
   // return a TGraphErrors for the KDE errors
   UInt_t n = npx;
   Double_t* x = new Double_t[n + 1];
   Double_t* ex = new Double_t[n + 1];
   Double_t* y = new Double_t[n + 1];
   Double_t* ey = new Double_t[n + 1];
   for (UInt_t i = 0; i <= n; ++i) {
      x[i] = xmin + i * (xmax - xmin) / n;
      y[i] = (*this)(x[i]);
      ex[i] = 0;
      ey[i] = this->GetError(x[i]);
   }
   TGraphErrors* ge = new TGraphErrors(n, &x[0], &y[0], &ex[0], &ey[0]);
   ge->SetName("kde_graph_error");
   ge->SetTitle("Errors");
   delete [] x;
   delete [] ex;
   delete [] y;
   delete [] ey;
   return ge;
}

void TKDE::DrawConfidenceInterval(TString& drawOpt,double cl) {
   // Draws the KDE and its confidence interval
   GetKDEFunction()->Draw(drawOpt.Data());
   TF1* upper = GetPDFUpperConfidenceInterval(cl);
   upper->SetLineColor(kBlue);
   upper->Draw(("same" + drawOpt).Data());
   TF1* lower = GetPDFLowerConfidenceInterval(cl);
   lower->SetLineColor(kRed);
   lower->Draw(("same" + drawOpt).Data());
   if (fUpperPDF) delete fUpperPDF;
   if (fLowerPDF) delete fLowerPDF;
   fUpperPDF = upper;
   fLowerPDF = lower;
}

Double_t TKDE::GetFixedWeight() const {
   // Returns the bandwidth for the non adaptive KDE
   Double_t result = -1.;
   if (fIteration == TKDE::kAdaptive) {
      this->Warning("GetFixedWeight()", "Fixed iteration option not enabled. Returning %f.", result);
   } else {
      result = fKernel->GetFixedWeight();
   }
   return result;
}

const Double_t *  TKDE::GetAdaptiveWeights() const {
   // Returns the bandwidths for the adaptive KDE
   if (fIteration != TKDE::kAdaptive) {
      this->Warning("GetFixedWeight()", "Adaptive iteration option not enabled. Returning a NULL pointer<");
      return 0;
   }
   if (fNewData) (const_cast<TKDE*>(this))->InitFromNewData();
   return &(fKernel->GetAdaptiveWeights()).front();
}

Double_t TKDE::TKernel::GetFixedWeight() const {
   // Returns the bandwidth for the non adaptive KDE
   return fWeights[0];
}

const std::vector<Double_t> & TKDE::TKernel::GetAdaptiveWeights() const {
   // Returns the bandwidth for the non adaptive KDE
   return fWeights;
}

Double_t TKDE::TKernel::operator()(Double_t x) const {
   // The internal class's unary function: returns the kernel density estimate
   Double_t result(0.0);
   UInt_t n = fKDE->fData.size();
   // case of bins or weighted data 
   Bool_t useBins = (fKDE->fBinCount.size() == n);
   Double_t nSum = (useBins) ? fKDE->fSumOfCounts : fKDE->fNEvents;
   // double dmin = 1.E10;
   // double xmin,bmin,wmin; 
   for (UInt_t i = 0; i < n; ++i) {
      Double_t binCount = (useBins) ? fKDE->fBinCount[i] : 1.0;
      result += binCount / fWeights[i] * (*fKDE->fKernelFunction)((x - fKDE->fData[i]) / fWeights[i]);
      if (fKDE->fAsymLeft) {
         result -= binCount / fWeights[i] * (*fKDE->fKernelFunction)((x - (2. * fKDE->fXMin - fKDE->fData[i])) / fWeights[i]);
      }
      if (fKDE->fAsymRight) {
         result -= binCount / fWeights[i] * (*fKDE->fKernelFunction)((x - (2. * fKDE->fXMax - fKDE->fData[i])) / fWeights[i]);
      }
      // if ( TMath::IsNaN(result) ) {
      //    printf("event %i count %f  weight %f  data % f x %f \n",i,binCount,fWeights[i],fKDE->fData[i],x );
      // }
      // if ( result <= 0 ) {
      //    printf("event %i count %f  weight %f  data % f x %f \n",i,binCount,fWeights[i],fKDE->fData[i],x );
      // }
      // if (std::abs(x -  fKDE->fData[i]) < dmin ) {
      //    xmin = x;
      //    bmin = binCount;
      //    wmin = fWeights[i];
      //    dmin = std::abs(x -  fKDE->fData[i]);
      // }
      // if (i < fKDE->fEvents.size() )
      // printf("data point %i  %f  %f  count %f weight % f result % f\n",i,fKDE->fData[i],fKDE->fEvents[i],binCount,fWeights[i], result);
   }
   if ( TMath::IsNaN(result) ) {
      fKDE->Warning("operator()","Result is NaN for  x %f \n",x);
    //xmin % f , %f, %f \n",result,x,xmin,bmin,wmin );
   }
   return result / nSum;
}

UInt_t TKDE::Index(Double_t x) const {
   // Returns the indices (bins) for the binned weights
   Int_t bin = Int_t((x - fXMin) * fWeightSize);
   if (bin == (Int_t)fData.size()) return --bin;
   if (fUseMirroring && (fMirrorLeft || !fMirrorRight)) {
      bin += fData.size() / (fMirrorLeft + fMirrorRight + 1);
   }
   if (bin > (Int_t)fData.size()) {
      return (Int_t)(fData.size()) - 1;
   } else if (bin <= 0) {
      return 0;
   }
   return bin;
}

Double_t TKDE::UpperConfidenceInterval(const Double_t* x, const Double_t* p) const {
   // Returns the pointwise upper estimated density
   Double_t f = (*this)(x);
   Double_t sigma = GetError(*x);
   Double_t prob = 1. - (1.-*p)/2;   // this is 1.-alpha/2
   Double_t z = ROOT::Math::normal_quantile(prob, 1.0);
   return f + z * sigma;
}

Double_t TKDE::LowerConfidenceInterval(const Double_t* x, const Double_t* p) const {
   // Returns the pointwise lower estimated density
   Double_t f = (*this)(x);
   Double_t sigma = GetError(*x);
   Double_t prob = (1.-*p)/2;    // this is alpha/2
   Double_t z = ROOT::Math::normal_quantile(prob, 1.0);
   return f + z * sigma;
}


Double_t TKDE::GetBias(Double_t x) const {
   // Returns the pointwise approximate estimated density bias
   ROOT::Math::WrappedFunction<const TKDE&> kern(*this);
   ROOT::Math::RichardsonDerivator rd;
   rd.SetFunction(kern);
   Double_t df2 = rd.Derivative2(x);
   Double_t weight = fKernel->GetWeight(x); // Bandwidth
   return  0.5 * fKernelSigmas2[fKernelType] * std::pow(weight, 2) * df2;
}
Double_t TKDE::GetError(Double_t x) const {
   // Returns the pointwise sigma of estimated density
   Double_t kernelL2Norm = ComputeKernelL2Norm();
   Double_t f = (*this)(x);
   Double_t weight = fKernel->GetWeight(x); // Bandwidth
   Double_t result = f * kernelL2Norm / (fNEvents * weight);
   return std::sqrt(result);
}

void TKDE::CheckKernelValidity() {
   // Checks if kernel has unit integral, mu = 0 and positive finite sigma conditions
   Double_t valid = kTRUE;
   Double_t unity = ComputeKernelIntegral();
   valid = valid && unity == 1.;
   if (!valid) {
      Error("CheckKernelValidity", "Kernel's integral is %f",unity);
   }
   Double_t mu = ComputeKernelMu();
   valid = valid && mu == 0.;
   if (!valid) {
      Error("CheckKernelValidity", "Kernel's mu is %f" ,mu);
   }
   Double_t sigma2 = ComputeKernelSigma2();
   valid = valid && sigma2 > 0 && sigma2 != std::numeric_limits<Double_t>::infinity();
   if (!valid) {
      Error("CheckKernelValidity", "Kernel's sigma2 is %f",sigma2);
   }
   if (!valid) {
      Error("CheckKernelValidity", "Validation conditions: the kernel's integral must be 1, the kernel's mu must be zero and the kernel's sigma2 must be finite positive to be a suitable kernel.");
      //exit(EXIT_FAILURE);
   }
}

Double_t TKDE::ComputeKernelL2Norm() const {
   // Computes the kernel's L2 norm
   ROOT::Math::IntegratorOneDim ig(ROOT::Math::IntegrationOneDim::kGAUSS);
   KernelIntegrand kernel(this, TKDE::KernelIntegrand::kNorm);
   ig.SetFunction(kernel);
   Double_t result = ig.Integral();
   return result;
}

Double_t TKDE::ComputeKernelSigma2() const {
   // Computes the kernel's sigma squared
   ROOT::Math::IntegratorOneDim ig( ROOT::Math::IntegrationOneDim::kGAUSS);
   KernelIntegrand kernel(this, TKDE::KernelIntegrand::kSigma2);
   ig.SetFunction(kernel);
   Double_t result = ig.Integral();
   return result;
}

Double_t TKDE::ComputeKernelMu() const {
   // Computes the kernel's mu
   ROOT::Math::IntegratorOneDim ig(ROOT::Math::IntegrationOneDim::kGAUSS);
   KernelIntegrand kernel(this, TKDE::KernelIntegrand::kMu);
   ig.SetFunction(kernel);
   Double_t result = ig.Integral();
   return result;
}

Double_t TKDE::ComputeKernelIntegral() const {
   // Computes the kernel's integral which ought to be unity
   ROOT::Math::IntegratorOneDim ig(ROOT::Math::IntegrationOneDim::kGAUSS);
   KernelIntegrand kernel(this, TKDE::KernelIntegrand::kUnitIntegration);
   ig.SetFunction(kernel);
   Double_t result = ig.Integral();
   return result;
}

void TKDE::ComputeDataStats() {
   /// in case of weights use
   if (!fEventWeights.empty() ) {
      // weighted data
      double x1 = fXMin - 0.001*(fXMax-fXMin);
      double x2 = fXMax + 0.001*(fXMax-fXMin);
      TH1D h1("temphist","", 500, x1, x2);
      h1.FillN(fEvents.size(), fEvents.data(), fEventWeights.data() );
      assert (h1.GetSumOfWeights() > 0) ;
      fMean = h1.GetMean();
      fSigma = h1.GetRMS();
      // compute robust sigma using midspread
      Double_t quantiles[2] = {0.0, 0.0};
      Double_t prob[2] = {0.25, 0.75};
      h1.GetQuantiles(2, quantiles, prob);
      Double_t midspread = quantiles[1] - quantiles[0];
      fSigmaRob = std::min(fSigma, midspread / 1.349); // Sigma's robust estimator
      //printf("weight case - stat: m = %f, s= %f, sr = %f \n",fMean, fSigma, midspread);
      return;
   }
   else {
      // compute statistics using the data
      SetMean();
      Double_t midspread = ComputeMidspread();
      SetSigma(midspread);
      //printf("un-weight case - stat: m = %f, s= %f, sr = %f \n",fMean, fSigma, fSigmaRob);
   }
}

Double_t TKDE::ComputeMidspread () {
   // Computes the inter-quartile range from the data
   std::sort(fEvents.begin(), fEvents.end());
   Double_t quantiles[2] = {0.0, 0.0};
   Double_t prob[2] = {0.25, 0.75};
   TMath::Quantiles(fEvents.size(), 2, &fEvents[0], quantiles, prob);
   Double_t lowerquartile = quantiles[0];
   Double_t upperquartile = quantiles[1];
   return upperquartile - lowerquartile;
}

void TKDE::SetUserCanonicalBandwidth() {
   // Computes the user's input kernel function canonical bandwidth
   fCanonicalBandwidths[kUserDefined] = std::pow(ComputeKernelL2Norm() / std::pow(ComputeKernelSigma2(), 2), 1. / 5.);
}

void TKDE::SetUserKernelSigma2() {
   // Computes the user's input kernel function sigma2
   fKernelSigmas2[kUserDefined] = ComputeKernelSigma2();
}

TKDE::KernelIntegrand::KernelIntegrand(const TKDE* kde, EIntegralResult intRes) : fKDE(kde), fIntegralResult(intRes) {
   // Internal class constructor
}

Double_t TKDE::KernelIntegrand::operator()(Double_t x) const {
   // Internal class unary function
   if (fIntegralResult == kNorm) {
      return std::pow((*fKDE->fKernelFunction)(x), 2);
   } else if (fIntegralResult == kMu) {
      return x * (*fKDE->fKernelFunction)(x);
   } else if (fIntegralResult == kSigma2) {
      return std::pow(x, 2) * (*fKDE->fKernelFunction)(x);
   } else if (fIntegralResult == kUnitIntegration) {
      return (*fKDE->fKernelFunction)(x);
   } else {
      return -1;
   }
}

TF1* TKDE::GetKDEFunction(UInt_t npx, Double_t xMin , Double_t xMax) {
   //Returns the estimated density
   TString name = "KDEFunc_"; name+= GetName();
   TString title = "KDE "; title+= GetTitle();
   if (xMin >= xMax) { xMin = fXMin; xMax = fXMax; }
   //Do not register the TF1 to global list
   bool previous = TF1::DefaultAddToGlobalList(kFALSE);
   TF1 * pdf = new TF1(name.Data(), this, xMin, xMax, 0);
   TF1::DefaultAddToGlobalList(previous);
   if (npx > 0) pdf->SetNpx(npx);
   pdf->SetTitle(title);
   return pdf;
}

TF1* TKDE::GetPDFUpperConfidenceInterval(Double_t confidenceLevel, UInt_t npx, Double_t xMin , Double_t xMax) {
   // Returns the upper estimated density
   TString name;
   name.Form("KDE_UpperCL%f5.3_%s",confidenceLevel,GetName());
   if (xMin >= xMax) { xMin = fXMin; xMax = fXMax; }
   TF1 * upperPDF = new TF1(name, this, &TKDE::UpperConfidenceInterval, xMin, xMax, 1);
   upperPDF->SetParameter(0, confidenceLevel);
   if (npx > 0) upperPDF->SetNpx(npx);
   TF1 * f =  (TF1*)upperPDF->Clone();
   delete upperPDF;
   return f;
}

TF1* TKDE::GetPDFLowerConfidenceInterval(Double_t confidenceLevel, UInt_t npx, Double_t xMin , Double_t xMax) {
   // Returns the upper estimated density
   TString name;
   name.Form("KDE_LowerCL%f5.3_%s",confidenceLevel,GetName());
   if (xMin >= xMax) { xMin = fXMin; xMax = fXMax; }
   TF1 * lowerPDF = new TF1(name, this, &TKDE::LowerConfidenceInterval, xMin, xMax, 1);
   lowerPDF->SetParameter(0, confidenceLevel);
   if (npx > 0) lowerPDF->SetNpx(npx);
   TF1 * f = (TF1*)lowerPDF->Clone();
   delete lowerPDF;
   return f;
}

TF1* TKDE::GetKDEApproximateBias(UInt_t npx, Double_t xMin , Double_t xMax) {
   // Returns the approximate bias
   TString name = "KDE_Bias_"; name += GetName();
   if (xMin >= xMax) { xMin = fXMin; xMax = fXMax; }
   TF1 * approximateBias = new TF1(name, this, &TKDE::ApproximateBias, xMin, xMax, 0);
   if (npx > 0) approximateBias->SetNpx(npx);
   TF1 * f =  (TF1*)approximateBias->Clone();
   delete approximateBias;
   return f;
}