
///\file "eventgenerator/pythia/decayer6/.README.txt"
///\brief Example decayer6 page

/*! \page Exampledecayer6 Example decayer6 

 This is an example of the external decayer implementation 
 with PYTHIA6.
 
 The complete PYTHIA6 documentation can be found at:
 http://home.thep.lu.se/~torbjorn/pythiaaux/recent.html
 
 The PYTHIA6 external decayer was originally developed within 
 the AliRoot framework, by Andreas Morsch (CERN).  \n
 The dependence on the ALICE software was taken off
 by Christian Holm Christensen.                    \n
 The dependence on the Root framework and the integration in 
 the Geant4 framework was done by Ivana Hrivnacova (IPN Orsay).
 
 <hr>

 The use of the external decayer is demonstrated with using the 
 classes from common examples repository, see below their complete 
 list.
 
 The G4Pythia6Decayer class provides the implementation of the
 G4VExternalDecayer interface with using PYTHIA6. In order
 to be able to use PYTHIA6, which is written in FORTRAN, 
 a C++ interface class Pythia6 is provided. This class
 interfaces only the PYTHIA6 functions relevant to decay.

 The G4Pythia6Decayer is instantiated in the 
 P6DExtDecayerPhysics::ConstructProcess() function where the external 
 decayer is set to G4Decay process for all particles.
 To demonstrate the decay with external decayer,
 the B- meson is defined in ExG4PrimaryGeneratorAction01,
 as it has no own decay table defined within Geant4.
 
 With PYTHIA6, it is possible to force a selected decay
 type. This selection can be chosen interactively via 
 the implemented Geant4 UI command:
\verbatim
/pythia6Decayer/forceDecayType decayType
\endverbatim
 where the available decay types  are listed in the EDecayType 
 enumaration.
 
 The classes Pythia6, G4Pythia6Decayer, G4Pythia6DecayerMessenger
 are independent from the example classes and can be reused 
 in another user application.
 
 Installation:
- 1. Download the PYTHIA6 source file from the PYTHIA6 download site:\n
   http://www.hepforge.org/downloads/pythia6
   
- 2A. With CMake: Build pythia6 library
 
  For a convenience a CMake file for building Pythia6 library from 
  the source is provided in
  examples/extended/eventgenerator/CMakeLists.txt.pythia6.
  Build the pythia6 library following the instructions in this file
  and then define the environment variables:
\verbatim
PYTHIA6          the path where pythia6 library is installed
PYTHIA6_VERSION  the pythia version 
\endverbatim

- 2B. With GNUmake: Define the environment variables: \n
\verbatim
PYTHIA6           the path to pythia-versionX.f source code
PYTHIA6_VERSION   the pythia version 
\endverbatim
    
  e.g. If you download pythia-6.4.26.f.gz and unzip it in $HOME,
       then you have to set:
  export PYTHIA6=$HOME
  export PYTHIA6_VERSION="6.4.26"
  
  pythia6 will be then compiled together with example code.
   
- 3. Compilation:\n
  Then the example is compiled in a standard way, see \ref README_HowToRun. \n
  Note that with GNUmake build, an additional step 'gmake setup' is 
  needed before 'gmake'. 
  
- 4. Execution:
\verbatim
% pythia6_decayer pythia6_decayer.in
\endverbatim                

This example uses the following user action classes from the extended examples common 
repository available in common subdirectory:
 - DetectorConstruction
 - GunPrimaryGeneratorAction

*/   
