Gabriele Cosmo
128 lines
4.6 KiB
C++
128 lines
4.6 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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// Abstract base class for multibody "phase space" generators. Subclasses
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// implement a specific algorithm, such as Kopylov, GENBOD, or Makoto's
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// NBody. Subclasses are used by G4HadPhaseSpaceGenerator.
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//
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// Author: Michael Kelsey (SLAC) <kelsey@slac.stanford.edu>
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#include "G4VHadDecayAlgorithm.hh"
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#include "G4HadronicException.hh"
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#include "G4PhysicalConstants.hh"
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#include "G4SystemOfUnits.hh"
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#include "G4ThreeVector.hh"
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#include "Randomize.hh"
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#include <algorithm>
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#include <iostream>
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#include <iterator>
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#include <numeric>
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#include <vector>
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// Initial state (rest mass) and list of final masses
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void G4VHadDecayAlgorithm::Generate(G4double initialMass,
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const std::vector<G4double>& masses,
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std::vector<G4LorentzVector>& finalState) {
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if (verboseLevel) G4cout << GetName() << "::Generate" << G4endl;
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// Initialization and sanity check
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finalState.clear();
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if (!IsDecayAllowed(initialMass, masses)) return;
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// Allow different procedures for two-body or N-body distributions
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if (masses.size() == 2U)
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GenerateTwoBody(initialMass, masses, finalState);
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else
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GenerateMultiBody(initialMass, masses, finalState);
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}
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// Base class does very simple validation of configuration
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G4bool G4VHadDecayAlgorithm::
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IsDecayAllowed(G4double initialMass,
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const std::vector<G4double>& masses) const {
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G4bool okay =
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(initialMass > 0. && masses.size() >= 2 &&
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initialMass >= std::accumulate(masses.begin(),masses.end(),0.));
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if (verboseLevel) {
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G4cout << GetName() << "::IsDecayAllowed? initialMass " << initialMass
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<< " " << masses.size() << " masses sum "
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<< std::accumulate(masses.begin(),masses.end(),0.) << G4endl;
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if (verboseLevel>1) PrintVector(masses," ",G4cout);
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G4cout << " Returning " << okay << G4endl;
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}
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return okay;
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}
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// Momentum function (c.f. PDK() function from CERNLIB W515)
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G4double G4VHadDecayAlgorithm::TwoBodyMomentum(G4double M0, G4double M1,
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G4double M2) const {
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G4double PSQ = (M0+M1+M2)*(M0+M1-M2)*(M0-M1+M2)*(M0-M1-M2);
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if (PSQ < 0.) {
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G4cout << GetName() << ": problem of decay of M(GeV) " << M0/GeV
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<< " to M1(GeV) " << M1/GeV << " and M2(GeV) " << M2/GeV
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<< " PSQ(MeV) " << PSQ/MeV << " < 0" << G4endl;
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// exception only if the problem is numerically significant
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if (PSQ < -CLHEP::eV) {
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throw G4HadronicException(__FILE__, __LINE__,"Error in decay kinematics");
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}
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PSQ = 0.;
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}
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return std::sqrt(PSQ)/(2.*M0);
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}
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// Convenience functions for uniform angular distributions
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G4double G4VHadDecayAlgorithm::UniformTheta() const {
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return std::acos(2.0*G4UniformRand() - 1.0);
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}
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G4double G4VHadDecayAlgorithm::UniformPhi() const {
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return twopi*G4UniformRand();
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}
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// Dump contents of vector to output
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void G4VHadDecayAlgorithm::
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PrintVector(const std::vector<G4double>& v,
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const G4String& vname, std::ostream& os) const {
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os << " " << vname << "(" << v.size() << ") ";
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std::copy(v.begin(), v.end(), std::ostream_iterator<G4double>(os, " "));
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os << std::endl;
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}
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