RooExponential.cxx

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/*****************************************************************************
 * Project: RooFit                                                           *
 * Package: RooFitModels                                                     *
 * @(#)root/roofit:$Id$
 * Authors:                                                                  *
 *   WV, Wouter Verkerke, UC Santa Barbara, verkerke@slac.stanford.edu       *
 *   DK, David Kirkby,    UC Irvine,         dkirkby@uci.edu                 *
 *                                                                           *
 * Copyright (c) 2000-2005, Regents of the University of California          *
 *                          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 RooExponential
    \ingroup Roofit
 
Exponential PDF. It computes
\f[
  \mathrm{RooExponential}(x, c) = \mathcal{N} \cdot \exp(c\cdot x),
\f]
where \f$ \mathcal{N} \f$ is a normalisation constant that depends on the
range and values of the arguments.
**/
 
#include "RooExponential.h"
 
#include "RooRealVar.h"
#include "RooBatchCompute.h"
 
 
#include <cmath>
 
using namespace std;
 
ClassImp(RooExponential);
 
////////////////////////////////////////////////////////////////////////////////
 
RooExponential::RooExponential(const char *name, const char *title,
                RooAbsReal& _x, RooAbsReal& _c) :
  RooAbsPdf(name, title),
  x("x","Dependent",this,_x),
  c("c","Exponent",this,_c)
{
}
 
////////////////////////////////////////////////////////////////////////////////
 
RooExponential::RooExponential(const RooExponential& other, const char* name) :
  RooAbsPdf(other, name), x("x",this,other.x), c("c",this,other.c)
{
}
 
////////////////////////////////////////////////////////////////////////////////
 
Double_t RooExponential::evaluate() const{
  return exp(c*x);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Compute multiple values of Exponential distribution.
void RooExponential::computeBatch(cudaStream_t* stream, double* output, size_t nEvents, RooFit::Detail::DataMap const& dataMap) const
{
  auto dispatch = stream ? RooBatchCompute::dispatchCUDA : RooBatchCompute::dispatchCPU;
  dispatch->compute(stream, RooBatchCompute::Exponential, output, nEvents, {dataMap.at(x),dataMap.at(c)});
}
 
 
Int_t RooExponential::getAnalyticalIntegral(RooArgSet& allVars, RooArgSet& analVars, const char* /*rangeName*/) const
{
  if (matchArgs(allVars,analVars,x)) return 1;
  if (matchArgs(allVars,analVars,c)) return 2;
  return 0 ;
}
 
////////////////////////////////////////////////////////////////////////////////
 
Double_t RooExponential::analyticalIntegral(Int_t code, const char* rangeName) const
{
  assert(code == 1 || code ==2);
 
  auto& constant  = code == 1 ? c : x;
  auto& integrand = code == 1 ? x : c;
 
  if (constant == 0.0) {
    return integrand.max(rangeName) - integrand.min(rangeName);
  }
 
  return (exp(constant*integrand.max(rangeName)) - exp(constant*integrand.min(rangeName)))
      / constant;
}