Examples for HepMC-Geant4 interface
                -----------------------------------

  This directory contains examples for using HepMC as an interface with 
various Monte Carlo event generators, such as PYTHIA. 
Note that HepMC can be currently compiled only with gcc, so examples in 
this directory were tested only with gcc.

Requirements for external software packages
-------------------------------------------
HepMC
  tested version : 1.21 (latest at 28/May/02)
  URL: http://mdobbs.home.cern.ch/mdobbs/HepMC/

PYTHIA
  tested version 6.205
  URL: http://www.thep.lu.se/~torbjorn/Pythia.html

What is provided
----------------
class HepMCG4Interface
  This class is derived from G4VPrimaryGenerator, and is a base class 
  for primary generation via HepMC object.

  protected members
  + virtual HepMC::GenEvent* GenerateHepMCEvent()
    Implement this method in his/her own concrete class.
    An empty event will be created in default.

  + void HepMC2G4(const HepMC::GenEvent* hepmcevt, G4Event* g4event)
    service method for conversion from HepMC::GenEvent to G4Event

  + virtual G4bool CheckVertexInsideWorld(const G4ThreeVector& pos) const
    We have to take care for the position of primaries because
    primary vertices outside the world volume give rise to G4Exception.
    If the default implementation is not adequate, an alternative 
    can be implemented in your own class.

  public members
  + virtual void GeneratePrimaryVertex(G4Event* anEvent)
    The default behavior is that a single HepMC event generated by
    GenerateHepMCEvent() will be converted to G4Event through HepMC2G4().

class HepMCG4AsciiReader / HepMCG4AsciiReaderMessenger
  (derived from HepMCG4Interface)
  This derived class is for reading primary information from 
  an Ascii file generated by HepMC.

class HepMCG4PythiaInterface / HepMCG4AsciiReaderMessenger
  (derived from HepMCG4Interface)
  This derived class is for directly calling PYTHIA functions. 
  Users can set parameters, initialize, generate, and terminate
  by command line operation.

Examples
--------
HepMCEx01
  This example is based on ExampleN04. Only part of the primary generator 
  action is replaced with new one.

HepMCEx02
  This is another example having the same generator action as HepMCEx01, 
  but much simpler user control.

Macros in examples
-----------------
hepmc_pygen.in
  process PYTHIA events(H->4mu) generated at every event.

hepmc_ascii.in
  read pregenerated events from HepMC Ascii file (data/example_MyPhyia.dat).

How to compile
--------------
To build these examples, directory names including HepMC and PYTHIA 
library have to be given in GNUmakefile.  Please modify the next two lines 
in GNUmakefile;

  HEPMC_DIR   := xxxxx    # HepMC installed directory
  CERNLIB_DIR := xxxxx    # directory including PYTHIA library

Notes
-----
We attached a sample HepMC Ascii data file, "data/example_MyPhyia.dat",
which contains ten PYTHIA events created by "data/example_MyPythia.cxx".