RooDstD0BG.cxx

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/*****************************************************************************
 * Project: RooFit                                                           *
 * Package: RooFitModels                                                     *
 * @(#)root/roofit:$Id$
 * Authors:                                                                  *
 *   UE, Ulrik Egede,     RAL,               U.Egede@rl.ac.uk                *
 *   MT, Max Turri,       UC Santa Cruz      turri@slac.stanford.edu         *
 *   CC, Chih-hsiang Cheng, Stanford         chcheng@slac.stanford.edu       *
 *   DK, David Kirkby,    UC Irvine,         dkirkby@uci.edu                 *
 *                                                                           *
 * Copyright (c) 2000-2005, Regents of the University of California          *
 *                          RAL 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)             *
 *****************************************************************************/

/** \class RooDstD0BG
    \ingroup Roofit

Special p.d.f shape that can be used to model the background of
D*-D0 mass difference distributions
**/

#include "RooDstD0BG.h"
#include "RooFit.h"
#include "RooAbsReal.h"
#include "RooRealVar.h"
#include "RooIntegrator1D.h"
#include "RooAbsFunc.h"
#include "RooVDTHeaders.h"
#include "BatchHelpers.h"

#include "TMath.h"

#include <cmath>
using namespace std;

ClassImp(RooDstD0BG);

////////////////////////////////////////////////////////////////////////////////

RooDstD0BG::RooDstD0BG(const char *name, const char *title,
             RooAbsReal& _dm, RooAbsReal& _dm0,
             RooAbsReal& _c, RooAbsReal& _a, RooAbsReal& _b) :
  RooAbsPdf(name,title),
  dm("dm","Dstar-D0 Mass Diff",this, _dm),
  dm0("dm0","Threshold",this, _dm0),
  C("C","Shape Parameter",this, _c),
  A("A","Shape Parameter 2",this, _a),
  B("B","Shape Parameter 3",this, _b)
{
}

////////////////////////////////////////////////////////////////////////////////

RooDstD0BG::RooDstD0BG(const RooDstD0BG& other, const char *name) :
  RooAbsPdf(other,name), dm("dm",this,other.dm), dm0("dm0",this,other.dm0),
  C("C",this,other.C), A("A",this,other.A), B("B",this,other.B)
{
}

////////////////////////////////////////////////////////////////////////////////

Double_t RooDstD0BG::evaluate() const
{
  Double_t arg= dm- dm0;
  if (arg <= 0 ) return 0;
  Double_t ratio= dm/dm0;
  Double_t val= (1- exp(-arg/C))* TMath::Power(ratio, A) + B*(ratio-1);

  return (val > 0 ? val : 0) ;
}

namespace {
//Author: Emmanouil Michalainas, CERN 9 SEPTEMBER 2019 

template<class Tdm, class Tdm0, class TC, class TA, class TB>
void compute(  size_t batchSize, double * __restrict output,
              Tdm DM, Tdm0 DM0, TC C, TA A, TB B)
{
  for (size_t i=0; i<batchSize; i++) {
    const double ratio = DM[i] / DM0[i];
    const double arg1 = (DM0[i]-DM[i]) / C[i];
    const double arg2 = A[i]*_rf_fast_log(ratio);
    output[i] = (1 -_rf_fast_exp(arg1)) * _rf_fast_exp(arg2) +B[i]*(ratio-1);
  }
  
  for (size_t i=0; i<batchSize; i++) {
    if (output[i]<0) output[i] = 0;
  }
}
};

RooSpan<double> RooDstD0BG::evaluateBatch(std::size_t begin, std::size_t batchSize) const {
  using namespace BatchHelpers;

  EvaluateInfo info = getInfo( {&dm, &dm0, &C, &A, &B}, begin, batchSize );
  if (info.nBatches == 0) {
    return {};
  }
  auto output = _batchData.makeWritableBatchUnInit(begin, batchSize);
  auto dmData = dm.getValBatch(begin, info.size);

  if (info.nBatches==1 && !dmData.empty()) {
    compute(info.size, output.data(), dmData.data(),
    BracketAdapter<double> (dm0),
    BracketAdapter<double> (C),
    BracketAdapter<double> (A),
    BracketAdapter<double> (B));
  }
  else {
    compute(info.size, output.data(),
    BracketAdapterWithMask (dm,dm.getValBatch(begin,info.size)),
    BracketAdapterWithMask (dm0,dm0.getValBatch(begin,info.size)),
    BracketAdapterWithMask (C,C.getValBatch(begin,info.size)),
    BracketAdapterWithMask (A,A.getValBatch(begin,info.size)),
    BracketAdapterWithMask (B,B.getValBatch(begin,info.size)));
  }
  return output;
}

////////////////////////////////////////////////////////////////////////////////
/// if (matchArgs(allVars,analVars,dm)) return 1 ;

Int_t RooDstD0BG::getAnalyticalIntegral(RooArgSet& /*allVars*/, RooArgSet& /*analVars*/, const char* /*rangeName*/) const
{
  return 0 ;
}

////////////////////////////////////////////////////////////////////////////////

Double_t RooDstD0BG::analyticalIntegral(Int_t code, const char* rangeName) const
{
  switch(code) {
  case 1:
    {
      Double_t min= dm.min(rangeName);
      Double_t max= dm.max(rangeName);
      if (max <= dm0 ) return 0;
      else if (min < dm0) min = dm0;

      Bool_t doNumerical= kFALSE;
      if ( A != 0 ) doNumerical= kTRUE;
      else if (B < 0) {
   // If b<0, pdf can be negative at large dm, the integral should
   // only up to where pdf hits zero. Better solution should be
   // solve the zero and use it as max.
   // Here we check this whether pdf(max) < 0. If true, let numerical
   // integral take care of. ( kind of ugly!)
   if ( 1- exp(-(max-dm0)/C) + B*(max/dm0 -1) < 0) doNumerical= kTRUE;
      }
      if ( ! doNumerical ) {
   return (max-min)+ C* exp(dm0/C)* (exp(-max/C)- exp(-min/C)) +
     B * (0.5* (max*max - min*min)/dm0 - (max- min));
      } else {
   // In principle the integral for a!=0  can be done analytically.
   // It involves incomplete Gamma function, TMath::Gamma(a+1,m/c),
   // which is not defined for a < -1. And the whole expression is
   // not stable for m/c >> 1.
   // Do numerical integral
   RooArgSet vset(dm.arg(),"vset");
   RooAbsFunc *func= bindVars(vset);
   RooIntegrator1D integrator(*func,min,max);
   return integrator.integral();
      }
    }
  }

  assert(0) ;
  return 0 ;
}