Geant4 User's Guide
For Application Developers
Getting Started with Geant4

2.9 How to Execute a Program

2.9.1 Introduction

A Geant4 application can be run either in

`purely hard-coded` batch mode
batch mode, but reading a macro of commands
interactive mode, driven by command lines
interactive mode via a Graphical User Interface

The last mode will be covered in Section 2.8. The first three modes are explained here.

2.9.2 'Hard-coded' Batch Mode

Below is an example of the main program for an application which will run in batch mode.

					   
int main()
{
  // Construct the default run manager
  G4RunManager* runManager = new G4RunManager;

  // set mandatory initialization classes
  runManager->SetUserInitialization(new ExN01DetectorConstruction);
  runManager->SetUserInitialization(new ExN01PhysicsList);

  // set mandatory user action class
  runManager->SetUserAction(new ExN01PrimaryGeneratorAction);

  // Initialize G4 kernel
  runManager->Initialize();

  // start a run
  int numberOfEvent = 1000;
  runManager->BeamOn(numberOfEvent);

  // job termination
  delete runManager;
  return 0;
}

Source listing 2.9.1
An example of the main() routine for an application which will run in batch mode.

Even the number of events in the run is `frozen`. To change this number you must at least recompile main().

2.9.3 Batch Mode with Macro File

Below is an example of the main program for an application which will run in batch mode, but reading a file of commands.

  
int main(int argc,char** argv) {

   // Construct the default run manager
  G4RunManager * runManager = new G4RunManager;
  
  // set mandatory initialization classes
  runManager->SetUserInitialization(new MyDetectorConstruction);
  runManager->SetUserInitialization(new MyPhysicsList);
  
  // set mandatory user action class
  runManager->SetUserAction(new MyPrimaryGeneratorAction);
  
  // Initialize G4 kernel
  runManager->Initialize();

  //read a macro file of commands
  G4UImanager * UI = G4UImanager::getUIpointer();
  G4String command = "/control/execute ";
  G4String fileName = argv[1];
  UI->applyCommand(command+fileName); 

  delete runManager;
  return 0;
}

Source listing 2.9.2
An example of the main() routine for an application which will run in batch mode, but reading a file of commands.

This example will be executed with the command:

    > myProgram  run1.mac

where myProgram is the name of your executable and run1.mac is a macro of commands located in the current directory, which could look like:

 
#
# Macro file for "myProgram.cc"
#
# set verbose level for this run
#
/run/verbose      2
/event/verbose    0
/tracking/verbose 1
#
# Set the initial kinematic and run 100 events
# electron 1 GeV to the direction (1.,0.,0.)
#
/gun/particle e-
/gun/energy 1 GeV
/run/beamOn 100

Source listing 2.9.3
A typical command macro.

Indeed, you can re-execute your program with different run conditions without recompiling anything.

Digression: many G4 category of classes have a verbose flag which controls the level of 'verbosity'.
Usually verbose=0 means silent. For instance

/run/verbose is for the RunManager
/event/verbose is for the EventManager
/tracking/verbose is for the TrackingManager
...etc...

2.9.4 Interactive Mode Driven by Command Lines

Below is an example of the main program for an application which will run interactively, waiting for command lines entered from the keyboard.

                           
int main(int argc,char** argv) {

  // Construct the default run manager
  G4RunManager * runManager = new G4RunManager;

  // set mandatory initialization classes
  runManager->SetUserInitialization(new MyDetectorConstruction);
  runManager->SetUserInitialization(new MyPhysicsList);
  
  // visualization manager
  G4VisManager* visManager = new G4VisExecutive;
  visManager->Initialize();
    
  // set user action classes
  runManager->SetUserAction(new MyPrimaryGeneratorAction);
  runManager->SetUserAction(new MyRunAction);
  runManager->SetUserAction(new MyEventAction);
  runManager->SetUserAction(new MySteppingAction);
  
  // Initialize G4 kernel
  runManager->Initialize();
  
  // Define UI terminal for interactive mode   
  G4UIsession * session = new G4UIterminal;    
  session->SessionStart();
  delete session;

  // job termination
  delete visManager;
  delete runManager;

  return 0;
}

Source listing 2.9.4
An example of the main() routine for an application which will run interactively, waiting for commands from the keyboard.

This example will be executed with the command:

  > myProgram

where myProgram is the name of your executable.

The G4 kernel will prompt:

  Idle>

and you can start your session. An example session could be:

Create an empty scene ("world" is default):

 
  Idle> /vis/scene/create

Add a volume to the scene:

 
  Idle> /vis/scene/add/volume

Create a scene handler for a specific graphics system. Change the next line to choose another graphic system:

 
  Idle> /vis/sceneHandler/create OGLIX

Create a viewer:

 
  Idle> /vis/viewer/create

Draw the scene, etc.:

 
  Idle> /vis/scene/notifyHandlers
  Idle> /run/verbose      0
  Idle> /event/verbose    0
  Idle> /tracking/verbose 1
  Idle> /gun/particle mu+
  Idle> /gun/energy 10 GeV
  Idle> /run/beamOn 1
  Idle> /gun/particle proton
  Idle> /gun/energy 100 MeV
  Idle> /run/beamOn 3		
  Idle> exit

For the meaning of the machine state Idle, see Section 3.4.2.

This mode is useful for running a few events in debug mode and visualizing them. Notice that the VisManager is created in the main(), and the visualization system is choosen via the command:

  /vis/sceneHandler/create OGLIX

2.9.5 General Case

Most of the examples in the $G4INSTALL/examples/ directory have the following main(), which covers cases 2 and 3 above. Thus, the application can be run either in batch or interactive mode.

int main(int argc,char** argv) {

  // Construct the default run manager
  G4RunManager * runManager = new G4RunManager;

  // set mandatory initialization classes
  N03DetectorConstruction* detector = new N03DetectorConstruction;
  runManager->SetUserInitialization(detector);
  runManager->SetUserInitialization(new N03PhysicsList);
  
#ifdef G4VIS_USE
  // visualization manager
  G4VisManager* visManager = new G4VisExecutive;
  visManager->Initialize();
#endif
    
  // set user action classes
  runManager->SetUserAction(new N03PrimaryGeneratorAction(detector));
  runManager->SetUserAction(new N03RunAction);
  runManager->SetUserAction(new N03EventAction);
  runManager->SetUserAction(new N03SteppingAction);
    
  // get the pointer to the User Interface manager 
    G4UImanager* UI = G4UImanager::GetUIpointer();  

  if (argc==1)   // Define UI terminal for interactive mode  
    { 
     G4UIsession * session = new G4UIterminal;
     UI->ApplyCommand("/control/execute prerunN03.mac");    
     session->SessionStart();
     delete session;
    }
  else           // Batch mode
    { 
     G4String command = "/control/execute ";
     G4String fileName = argv[1];
     UI->ApplyCommand(command+fileName);
    }

  // job termination
#ifdef G4VIS_USE
  delete visManager;
#endif
  delete runManager;

  return 0;
}

Source listing 2.9.5
The typical main() routine from the examples directory.

Notice that the visualization system is under the control of the precompiler variable G4VIS_USE. Notice also that, in interactive mode, few intializations have been put in the macro prerunN03.mac which is executed before the session start.

 
 # Macro file for the initialization phase of "exampleN03.cc"
 #
 # Sets some default verbose flags
 # and initializes the graphics.
 #
 /control/verbose 2
 /control/saveHistory
 /run/verbose 2
 #
 /run/particle/dumpCutValues
 #
 # Create empty scene ("world" is default)
 /vis/scene/create
 #
 # Add volume to scene
 /vis/scene/add/volume
 #
 # Create a scene handler for a specific graphics system
 # Edit the next line(s) to choose another graphic system
 #
 #/vis/sceneHandler/create DAWNFILE
 /vis/sceneHandler/create OGLIX
 #
 # Create a viewer
 /vis/viewer/create
 #
 # Draw scene
 /vis/scene/notifyHandlers
 #
 # for drawing the tracks
 # if too many tracks cause core dump => storeTrajectory 0
 /tracking/storeTrajectory 1
 #/vis/scene/include/trajectories

Source listing 2.9.6
The prerunN03.mac macro.

Also, this example demonstrates that you can read and execute a macro interactively:

 
  Idle> /control/execute  mySubMacro.mac

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