$Id: README.N03,v 1.1 2007/05/26 00:18:27 tkoi Exp $
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     =========================================================
     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
     =========================================================

                            ExampleN03
                            ----------

	This example simulates a simple Sampling Calorimeter setup.
	
 1- GEOMETRY DEFINITION
 
 	The calorimeter is a box made of a given number of layers. A layer
 	consists of an absorber plate and of a detection gap. The layer is
 	replicated.
 	
 	Six parameters define the calorimeter :
 	- the material of the absorber,
	- the thickness of an absorber plate,
 	- the material of the detection gap,
 	- the thickness of a  gap,
 	- the number of layers,
 	- the transverse size of the calorimeter (the input face is a square). 
 	
 	In addition a transverse uniform magnetic field can be applied.
 	
 	The default geometry is constructed in DetectorConstruction class,
 	but all of the above parameters can be modified interactively via
 	the commands defined in the DetectorMessenger class.


	|<----layer 0---------->|<----layer 1---------->|<----layer 2---------->|
	|			|			|			|
	==========================================================================
	||		|	||		|	||		|	||
	||		|	||		|	||		|	||
	||   absorber 	|  gap	||   absorber 	|  gap	||   absorber 	|  gap	||
	||		|	||		|	||		|	||
	||		|	||		|	||		|	||
 beam	||		|	||		|	||		|	||
======>	||		|	||		|	||		|	||
	||		|	||		|	||		|	||
	||		|	||		|	||		|	||
	||		|	||		|	||		|	||
	||		|	||		|	||		|	||
	||    		| 	||    		| 	||    		| 	||
	==========================================================================
	
 	NB. The thickness of the absorber or of the gap can be set to zero
 	    (but not together), and the number of layers to 1. In this case we
 	    have a unique homogeneous block of matter, which looks like
 	    a bubble chamber rather than a calorimeter ...
 	    (see the macro of commands: newgeom.mac)
 	    
 2- AN EVENT : THE PRIMARY GENERATOR
 
 	The primary kinematic consists of a single particle which hits the
 	calorimeter perpendicular to the input face. The type of the particle
 	and its energy are set in the PrimaryGeneratorAction class, and can
 	be changed via the G4 build-in commands of ParticleGun class (see
 	the macros provided with this example).
 	
 	In addition one can choose randomly the impact point of the incident
 	particle. The corresponding interactive command is built in
 	PrimaryGeneratorMessenger class (see run2.mac).
 	
 	A RUN is a set of events.
 	
 				
 3- VISUALIZATION
 
 	The Visualization Manager is set in the main().
 	The initialisation of the drawing is done via a set of /vis/ commands
        in the macro vis.mac. This macro is automatically read from 
 	the main in case of interactive running mode.

        By default, vis.mac opens a DAWNFILE, suitable for viewing in DAWN,
	and an OGLX for OpenGl.
        You can switch to other graphics systems by commenting out this line
        and instead uncommenting one of the other /vis/open statements, such as
        HepRepFile or HepRepXML.
	
	The DAWNFILE, HepRepFile and HepRepXML drivers are always available 
	(since they require no external libraries), but the OGLIX driver 
	requires:
	    1- the visualisation & interfaces categories have been compiled
	       with the environment variable G4VIS_BUILD_OPENGLX_DRIVER.
	    2- exampleN03.cc has been compiled with G4VIS_USE_OPENGLX.

	The HepRepXML driver outputs a zip file that can be unzipped into 
	several individual HepRep files, each viewable in WIRED.

	For more information on visualization, including information on how to
	install and run DAWN, OpenGL and WIRED, see the visualization tutorials
	on the Geant4 Workshop Tutorial CD available at:
	http://geant4.slac.stanford.edu/g4cd/Welcome.html
 	
 	The detector has a default view which is a longitudinal view of the 
 	calorimeter.
 	
 	The tracks are drawn at the end of event, and erased at the end of run.
 	Optionaly one can choose to draw all particles, only the charged,
 	or neutral or none. This command is build in EventActionMessenger class.
 	
	Additional visualization tutorial macros are available in the visTutor
	subdirectory.  They can be tried as:
               % $G4BINDIR/exampleN03
	       idle > /control/execute visTutor/exN03VisX.mac
        For details, see comment lines  described in the macro files.
        These macros are designed to help your understanding the User's Guide.


 4- PHYSICS DEMO
 
 	The particle's type and the physic processes which will be available
 	in this example are set in PhysicsList class.
 	
 	In addition the build-in interactive command:
	         /process/(in)activate processName
 	allows to activate/inactivate the processes one by one.
 	Then one can well visualize the processes one by one, especially 
 	in the bubble chamber setup with a transverse magnetic field.
	(see run2.mac and newgeom.mac)
 
 	As a homework try to visualize a gamma conversion alone, 
 	or the effect of the multiple scattering.
	
 5- RANDOM NUMBERS HANDLING
 
 	CLHEP provides several random number engines. In this example the Ranecu
	engine is choosen at beginning of the main (exampleN03.cc).
	
	By default, G4RunManager does not save the rndm seed.
	To do so the user must set in BeginOfRunAction:
	G4RunManager::GetRunManager()->SetRandomNumberStore(true);
	
	Then the rndm seed is systematically saved at beginning of run
	(currentRun.rndm) and beginning of event (currentEvent.rndm)
	Therefore, in case of abnormal end, the seed of the last event processed
	is available in currentEvent.rndm
	
	Even in case of normal run processing, the user may wish to preserve the
	rndm seed of selected events. At any time in the event, put the
	following statement:
	if (condition) G4RunManager::GetRunManager()->rndmSaveThisEvent();
	currentEvent.rndm will be copied to runXXevntYY.rndm
	(see ExN03SteppingAction::UserSteppingAction() )
	
	To restart a run from a given rndm seed, use the UI command :
	/random/resetEngineFrom  fileName 
	
	The macro rndmSeed.mac shows how to save and reset the random number
	seed between runs, from UI commands.	
	
 6- USER INTERFACES
  
        The default command interface, called G4UIterminal, is done via
	standart cin/G4cout.
	On Linux and Sun-cc on can use a smarter command interface G4UItcsh.
	It is enough to set the environment variable G4UI_USE_TCSH
	
	On can use a Motif driven command interface (called G4UIXm) if:
	  1- interfaces category has been compiled with G4UI_BUILD_XM_SESSION
	  2- exampleN03.cc has been compiled with G4UI_USE_XM. 
 
      	
 7- HOW TO START ?
 
 	- compile and link to generate an executable
 		% cd N03
 		% gmake
 		
 	- execute N03 in 'batch' mode from macro files
 		% exampleN03   run1.mac
 		
 	- execute N03 in 'interactive mode' with visualization
 		% exampleN03
 		....
 		Idle>      ---> type your commands. For instance:
		Idle> /run/beamOn 
		....
		Idle> /run/beamOn 10
		....				
 		Idle> /control/execute newgeom.mac
 		....
 		Idle> exit
 	
 	  
 	
