HypoTestInverterResult.cxx

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// @(#)root/roostats:$Id: HypoTestInverterResult.cxx 36230 2010-10-09 20:21:02Z wouter $
// Author: Kyle Cranmer, Lorenzo Moneta, Gregory Schott, Wouter Verkerke
/*************************************************************************
 * Copyright (C) 1995-2008, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/


/**
   HypoTestInverterResult class: holds the array of hypothesis test results and compute a confidence interval.
   Based on the RatioFinder code available in the RooStatsCms package developed by Gregory Schott and Danilo Piparo
   Ported and adapted to RooStats by Gregory Schott
   Some contributions to this class have been written by Matthias Wolf (error estimation)
**/


// include header file of this class 
#include "RooStats/HypoTestInverterResult.h"

#include "RooStats/HypoTestInverterPlot.h"
#include "RooStats/HybridResult.h"

#include "TF1.h"
#include "TGraphErrors.h"

ClassImp(RooStats::HypoTestInverterResult)

using namespace RooStats;


HypoTestInverterResult::HypoTestInverterResult(const char * name ) :
   SimpleInterval(name),
   fUseCLs(false),
   fInterpolateLowerLimit(true),
   fInterpolateUpperLimit(true)
{
  // default constructor
}


HypoTestInverterResult::HypoTestInverterResult( const char* name,
                                                const RooRealVar& scannedVariable,
                                                double cl ) :
   SimpleInterval(name,scannedVariable,-999,999,cl), 
   fUseCLs(false),
   fInterpolateLowerLimit(true),
   fInterpolateUpperLimit(true)
{
  // constructor 
   fYObjects.SetOwner();
}


HypoTestInverterResult::~HypoTestInverterResult()
{
   // destructor
   // no need to delete explictly the objects in the TList since the TList owns the objects
}


bool HypoTestInverterResult::Add( const HypoTestInverterResult& /* otherResult */  )
{
  /// Merge this HypoTestInverterResult with another
  /// HypoTestInverterResult passed as argument

  std::cout << "Sorry, this function is not yet implemented\n";

  return true;
}

 
double HypoTestInverterResult::GetXValue( int index ) const
{
  if ( index >= ArraySize() || index<0 ) {
    std::cout << "Problem: You are asking for an impossible array index value\n";
    return -999;
  }

  return fXValues[index];
}

double HypoTestInverterResult::GetYValue( int index ) const
{
  if ( index >= ArraySize() || index<0 ) {
    std::cout << "Problem: You are asking for an impossible array index value\n";
    return -999;
  }

  if (fUseCLs) 
    return ((HybridResult*)fYObjects.At(index))->CLs();
  else 
    return ((HybridResult*)fYObjects.At(index))->AlternatePValue();  // CLs+b
}

double HypoTestInverterResult::GetYError( int index ) const
{
  if ( index >= ArraySize() || index<0 ) {
    std::cout << "Problem: You are asking for an impossible array index value\n";
    return -999;
  }

  if (fUseCLs) 
    return ((HybridResult*)fYObjects.At(index))->CLsError();
  else 
    return ((HybridResult*)fYObjects.At(index))->CLsplusbError();
}

HypoTestResult* HypoTestInverterResult::GetResult( int index ) const
{
  if ( index >= ArraySize() || index<0 ) {
    std::cout << "Problem: You are asking for an impossible array index value\n";
    return 0;
  }

  return ((HypoTestResult*) fYObjects.At(index));
}

double HypoTestInverterResult::FindInterpolatedLimit(double target)
{
  std::cout << "Interpolate the upper limit between the 2 results closest to the target confidence level" << endl;

  if (ArraySize()<2) {
    std::cout << "Error: not enough points to get the inverted interval\n";
    if (target<0.5) return ((RooRealVar*)fParameters.first())->getMax();
    else return ((RooRealVar*)fParameters.first())->getMin();
  }

  double v1 = fabs(GetYValue(0)-target);
  int i1 = 0;
  double v2 = fabs(GetYValue(1)-target);
  int i2 = 1;

  if (ArraySize()>2)
    for (int i=2; i<ArraySize(); i++) {
      double vt = fabs(GetYValue(i)-target);
      if ( vt<v1 || vt<v2 ) {
        if ( v1<v2 ) {
          v2 = vt;
          i2 = i;
        } else {
          v1 = vt;
          i1 = i;
        }
      }
    }

  return GetXValue(i1)+(target-GetYValue(i1))*(GetXValue(i2)-GetXValue(i1))/(GetYValue(i2)-GetYValue(i1));
}

int HypoTestInverterResult::FindClosestPointIndex(double target)
{
  // find the object with the smallest error that is < 1 sigma from the target
  double bestValue = fabs(GetYValue(0)-target);
  int bestIndex = 0;
  for (int i=1; i<ArraySize(); i++) {
    if ( fabs(GetYValue(i)-target)<GetYError(i) ) { // less than 1 sigma from target CL
      double value = fabs(GetYValue(i)-target);
      if ( value<bestValue ) {
        bestValue = value;
        bestIndex = i;
      }
    }
  }

  return bestIndex;
}

Double_t HypoTestInverterResult::LowerLimit()
{
   //std::cout << "finding point with cl = " << 1-(1-ConfidenceLevel())/2 << endl;
  if ( fInterpolateLowerLimit ){
    fLowerLimit = FindInterpolatedLimit(1-(1-ConfidenceLevel())/2);
  } else {
    fLowerLimit = GetXValue( FindClosestPointIndex(1-(1-ConfidenceLevel())/2) );
  }
  return fLowerLimit;
}

Double_t HypoTestInverterResult::UpperLimit()
{
   //std::cout << "finding point with cl = " << (1-ConfidenceLevel())/2 << endl;
  if ( fInterpolateUpperLimit ) {
     fUpperLimit = FindInterpolatedLimit((1-ConfidenceLevel())/2);
  } else {
     fUpperLimit = GetXValue( FindClosestPointIndex((1-ConfidenceLevel())/2) );
  }
  return fUpperLimit;
}

Double_t HypoTestInverterResult::CalculateEstimatedError(double target)
{
  // Return an error estimate on the upper limit.  This is the error on
  // either CLs or CLsplusb divided by an estimate of the slope at this
  // point.

  if (ArraySize()<2) {
    std::cout << "not enough points to get the inverted interval\n";
  }
 
  // The graph contains the points sorted by their x-value
  HypoTestInverterPlot plot("plot", "", this);
  TGraphErrors* graph = plot.MakePlot();
  double* xs = graph->GetX();
  const double minX = xs[0];
  const double maxX = xs[ArraySize()-1];

  TF1 fct("fct", "exp([0] * x + [1] * x**2)", minX, maxX);
  graph->Fit(&fct,"Q");

  int index = FindClosestPointIndex(target);
  double m = fct.Derivative( GetXValue(index) );
  double theError = fabs( GetYError(index) / m);

  delete graph;

  return theError;
}


Double_t HypoTestInverterResult::LowerLimitEstimatedError()
{
   //std::cout << "The HypoTestInverterResult::LowerLimitEstimatedError() function evaluates only a rought error on the upper limit. Be careful when using this estimation\n";
  if (fInterpolateLowerLimit) std::cout << "The lower limit was an interpolated results... in this case the error is even less reliable (the Y-error bars are currently not used in the interpolation)\n";

  return CalculateEstimatedError(ConfidenceLevel()/2);
}


Double_t HypoTestInverterResult::UpperLimitEstimatedError()
{
   //std::cout << "The HypoTestInverterResult::UpperLimitEstimatedError() function evaluates only a rought error on the upper limit. Be careful when using this estimation\n";
  if (fInterpolateUpperLimit) std::cout << "The upper limit was an interpolated results... in this case the error is even less reliable (the Y-error bars are currently not used in the interpolation)\n";

  return CalculateEstimatedError((1-ConfidenceLevel())/2);
}

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