FlowMapper.h

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// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
// All rights not expressly granted are reserved.
//
// This software is distributed under the terms of the GNU General Public
// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
//
// In applying this license CERN does not waive the privileges and immunities
// granted to it by virtue of its status as an Intergovernmental Organization
// or submit itself to any jurisdiction.
 
#ifndef ALICEO2_EVENTGEN_FLOWMAPPER_H_
#define ALICEO2_EVENTGEN_FLOWMAPPER_H_
 
#include "TH1D.h"
#include "TH3D.h"
#include "TF1.h"
 
namespace o2
{
namespace eventgen
{
 
/*****************************************************************/
/*****************************************************************/
 
// this class implements a mapper that introduces a synthetic v2
// into an otherwise uniform initial distribution of phis. It can
// be used, for instance, to create artificial flow of realistic
// intensity in PYTHIA simulations.
 
// The input histograms are to be read from the CCDB and can
// be customized if necessary. Multiple copies of this mapper
// could be used in case different species should have different
// additional flow.
 
// N.B.: the main advantages of this mapper is that:
//       1) it preserves total number of particles
//       2) it retains a (distorted) event structure from
//          an original event generator (e.g. PYTHIA)
 
class FlowMapper
{
 public:
  // Constructor
  FlowMapper();
 
  void SetNBinsPhi(long mBinsPhiProvided) { mBinsPhi = mBinsPhiProvided; };
  void SetPrecision(long mPrecisionProvided) { mPrecision = mPrecisionProvided; };
  void SetDerivative(long mDerivativeProvided) { mDerivative = mDerivativeProvided; };
 
  void CreateLUT(TH1D* mhv2vsPt, TH1D* mhEccVsB);
 
  Double_t MapPhi(Double_t lPhiInput, Double_t b, Double_t pt);
 
  long mBinsPhi;             // number of phi bins to use
  double mPrecision = 1e-6;  // precision threshold for numerical inversion success
  double mDerivative = 1e-4; // delta-X for derivative calculation
 
  // Cumulative function to be inverted
  std::unique_ptr<TF1> mCumulative;
 
  // the look-up table
  std::unique_ptr<TH3D> mhLUT;
 
  ClassDef(FlowMapper, 1);
};
 
/*****************************************************************/
/*****************************************************************/
 
} // namespace eventgen
} // namespace o2
 
#endif /* ALICEO2_EVENTGEN_FLOWMAPPER_H_ */