RooBifurGauss.cxx

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/*****************************************************************************
 * Project: RooFit                                                           *
 * Package: RooFitModels                                                     *
 * @(#)root/roofit:$Id: RooBifurGauss.cxx 24286 2008-06-16 15:47:04Z wouter $
 * Authors:                                                                  *
 *   Abi Soffer, Colorado State University, abi@slac.stanford.edu            *
 *                                                                           *
 * Copyright (c) 2000-2005, Regents of the University of California,         *
 *                          Colorado State University                        *
 *                          and Stanford University. All rights reserved.    *
 *                                                                           *
 * Redistribution and use in source and binary forms,                        *
 * with or without modification, are permitted according to the terms        *
 * listed in LICENSE (http://roofit.sourceforge.net/license.txt)             *
 *****************************************************************************/
#include "RooFit.h"

//////////////////////////////////////////////////////////////////////////////
//
// BEGIN_HTML
// Bifurcated Gaussian p.d.f with different widths on left and right
// side of maximum value
// END_HTML
//


#include "Riostream.h"
#include "TMath.h"
#include <math.h>

#include "RooBifurGauss.h"
#include "RooAbsReal.h"
#include "RooMath.h"

ClassImp(RooBifurGauss)

static const char rcsid[] =
"$Id: RooBifurGauss.cxx 24286 2008-06-16 15:47:04Z wouter $";


//_____________________________________________________________________________
RooBifurGauss::RooBifurGauss(const char *name, const char *title,
                             RooAbsReal& _x, RooAbsReal& _mean,
                             RooAbsReal& _sigmaL, RooAbsReal& _sigmaR) :
  RooAbsPdf(name, title), 
  x     ("x"     , "Dependent"  , this, _x),
  mean  ("mean"  , "Mean"       , this, _mean),
  sigmaL("sigmaL", "Left Sigma" , this, _sigmaL),
  sigmaR("sigmaR", "Right Sigma", this, _sigmaR)

{
}


//_____________________________________________________________________________
RooBifurGauss::RooBifurGauss(const RooBifurGauss& other, const char* name) : 
  RooAbsPdf(other,name), x("x",this,other.x), mean("mean",this,other.mean),
  sigmaL("sigmaL",this,other.sigmaL), sigmaR("sigmaR", this, other.sigmaR)
{
}


//_____________________________________________________________________________
Double_t RooBifurGauss::evaluate() const {

  Double_t arg = x - mean;

  Double_t coef(0.0);

  if (arg < 0.0){
    if (TMath::Abs(sigmaL) > 1e-30) {
      coef = -0.5/(sigmaL*sigmaL);
    }
  } else {
    if (TMath::Abs(sigmaR) > 1e-30) {
      coef = -0.5/(sigmaR*sigmaR);
    }
  }
    
  return exp(coef*arg*arg);
}


//_____________________________________________________________________________
Int_t RooBifurGauss::getAnalyticalIntegral(RooArgSet& allVars, RooArgSet& analVars, const char* /*rangeName*/) const 
{
  if (matchArgs(allVars,analVars,x)) return 1 ;
  return 0 ;
}


//_____________________________________________________________________________
Double_t RooBifurGauss::analyticalIntegral(Int_t code, const char* rangeName) const 
{
  switch(code) {
  case 1: 
    {
      static Double_t root2 = sqrt(2.) ;
      static Double_t rootPiBy2 = sqrt(atan2(0.0,-1.0)/2.0);
      
      Double_t coefL(0.0), coefR(0.0);
      if (TMath::Abs(sigmaL) > 1e-30) {
        coefL = -0.5/(sigmaL*sigmaL);
      }

      if (TMath::Abs(sigmaR) > 1e-30) {
        coefR = -0.5/(sigmaR*sigmaR);
      }

      Double_t xscaleL = root2*sigmaL;
      Double_t xscaleR = root2*sigmaR;

      Double_t integral = 0.0;
      if(x.max(rangeName) < mean)
      {
        integral = sigmaL * ( RooMath::erf((x.max(rangeName) - mean)/xscaleL) - RooMath::erf((x.min(rangeName) - mean)/xscaleL) );
      }
      else if (x.min(rangeName) > mean)
      {
        integral = sigmaR * ( RooMath::erf((x.max(rangeName) - mean)/xscaleR) - RooMath::erf((x.min(rangeName) - mean)/xscaleR) );
      }
      else
      {
        integral = sigmaR*RooMath::erf((x.max(rangeName) - mean)/xscaleR) - sigmaL*RooMath::erf((x.min(rangeName) - mean)/xscaleL);
      }
      //      return rootPiBy2*(sigmaR*RooMath::erf((x.max(rangeName) - mean)/xscaleR) - 
      //                        sigmaL*RooMath::erf((x.min(rangeName) - mean)/xscaleL));
      return integral*rootPiBy2;
    }
  }  

  assert(0) ; 
  return 0 ; // to prevent compiler warnings
}

---