EvtDalitzFlatPdf.cc

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#include "EvtPatches.hh"
/*******************************************************************************
 * Project: BaBar detector at the SLAC PEP-II B-factory
 * Package: EvtGenBase
 *    File: $Id: EvtDalitzFlatPdf.cc,v 1.1.1.2 2007/10/26 05:03:14 pingrg Exp $
 *  Author: Alexei Dvoretskii, dvoretsk@slac.stanford.edu, 2001-2002
 *
 * Copyright (C) 2002 Caltech
 *******************************************************************************/
 
#include "EvtDalitzFlatPdf.hh"
#include "EvtPatches.hh"
#include <cstdlib>
 
EvtDalitzFlatPdf::EvtDalitzFlatPdf( const EvtDalitzPlot& dp )
    : EvtPdf<EvtDalitzPoint>(), _dp( dp ) {}
 
EvtDalitzFlatPdf::EvtDalitzFlatPdf( const EvtDalitzFlatPdf& other )
    : EvtPdf<EvtDalitzPoint>( other ), _dp( other._dp ) {}
 
EvtDalitzFlatPdf::~EvtDalitzFlatPdf() {}
 
EvtPdf<EvtDalitzPoint>* EvtDalitzFlatPdf::clone() const {
  return new EvtDalitzFlatPdf( *this );
}
 
double EvtDalitzFlatPdf::pdf( const EvtDalitzPoint& ) const { return 1.; }
 
EvtValError EvtDalitzFlatPdf::compute_integral( int N ) const {
  return EvtValError( _dp.getArea( N ), 0. );
}
 
EvtDalitzPoint EvtDalitzFlatPdf::randomPoint() {
  // To obtain a uniform distribution generate
  // in terms of q's. Generate in a box that circumscribes the
  // Dalitz plot. Accept points inside. If there are two
  // many unsuccessful attempts it's a hint that the Dalitz plot
  // area is tiny compared to the box. It's a pathological
  // case. Abort.
 
  EvtCyclic3::Pair pair1 = EvtCyclic3::BC;
  EvtCyclic3::Pair pair2 = EvtCyclic3::CA;
 
  int n        = 0;
  int maxTries = 1000;
  while ( n++ < maxTries )
  {
 
    double q1 = EvtRandom::Flat( _dp.qAbsMin( pair1 ), _dp.qAbsMax( pair2 ) );
    double q2 = EvtRandom::Flat( _dp.qAbsMin( pair2 ), _dp.qAbsMax( pair2 ) );
 
    EvtDalitzCoord point( pair1, q1, pair2, q2 );
    EvtDalitzPoint x( _dp, point );
 
    if ( x.isValid() ) return x;
  }
 
  printf( "No point generated for dalitz plot after %d tries\n", maxTries );
  abort();
}