G4MPI is a native interface with MPI libraries. The directory contains a Geant4 UI library and a couple of parallelized examples. Using this interface, users applications can be parallelized with different MPI compliant libraries, such as OpenMPI, LAM/MPI, MPICH2 and so on.

System Requirements:

MPI Library

The MPI interface can work with MPI-compliant libraries, such as Open MPI, LAM/MPI, Intel MPI etc.

For example, the information about Open MPI can be obtained from http://www.open-mpi.org/

CMake

CMake is used to build G4MPI library, that co-works with Geant4 build system.

Optional

ROOT for histogramming/analysis

How to build G4MPI

To build G4MPI library, use CMake on Geant4 library installed with CMake build.

Check CMakeList.txt, especially the following two variables should be taken care to match your MPI library

eg.  
set(CMAKE_CXX_COMPILER mpicxx)  
#set(CMAKE_CXX_INCLUDE_PATH ) set if necessary

Follow these commands,

> cd source
> mkdir build
> cd build
> cmake -DGeant4_DIR=<your Geant4 install path>/lib64/Geant4-V.m.n ..
  (V.m.n is the version of Geant4, eg. Geant4-9.6.0)
> make
> make install

The library and header files will be installed on the installation directory of Geant4.

How to use

How to make parallel applications

An example of a main program:

#include "G4MPImanager.hh"
#include "G4MPIsession.hh"

int main(int argc,char** argv)
{
  // At first, G4MPImanager/G4MPIsession should be created.
  G4MPImanager* g4MPI= new G4MPImanager(argc,argv);
      
  // MPI session (G4MPIsession) instead of G4UIterminal
  G4MPIsession* session= g4MPI-> GetMPIsession();
      
  // user application setting
  G4RunManager* runManager= new G4RunManager();

  ....

  // After user application setting, just start a MPI session.
  MPIsession treats both interactive and batch modes.
  session-> SessionStart();

  // Finally, terminate the program
  delete g4MPI;
  delete runManager;
}

Notes about session shell

LAM/MPI users can use "G4tcsh" as an interactive session shell. For other users (Open MPI/MPICH2), plesae use G4csh (default).

In case of OpenMPI, LD_LIBRARY_PATH for OpenMPI runtime libraries should be set at run time. Alternatively, you can add this path to the dynamic linker configuration using ldconfig. (needs sys-admin authorization)

MPI runtime Environment

Make hosts/cluster configuration of your MPI environment.
Launch MPI runtime environment, typically executing lamboot (LAM) / mpdboot (MPICH2).

How to run

For example,

> mpiexec -n # <your application>

Instead, mpirun command is more convenient for LAM users.

MPI G4UI commands

G4UI commands handling the G4MPI interface are placed in /mpi/.

Command directory path : /mpi/
    
Guidance :
MPI control commands
    
 Sub-directories :
 Commands :
   verbose *        Set verbose level.
   status *         Show mpi status.
   execute *        Execute a macro file. (=/control/execute)
   beamOn *         Start a parallel run w/ thread.
   .beamOn *        Start a parallel run w/o thread.
   masterWeight *   Set weight for master node.
   showSeeds *      Show seeds of MPI nodes.
   setMasterSeed *  Set a master seed for the seed generator.
   setSeed *        Set a seed for a specified node.

Notes:

While "/run/beamOn" and "/mpi/beamOn" commands invoke beam-on in background, so you can input UI commands even while event processing. Note that drawing tracks in OpenGL with these commands causes a crash. Please use /mpi/.beamOn command instead.

The original "/control/execute" and "/run/beamOn" are overwritten with "/mpi/execute" and "/mpi/beamOn" commands respectively, that are customized for the MPI interface.

Examples

There are a couple of examples for Geant4 MPI applications.

In some cases, you need to set some additional environment variables for running examples:

G4LEDATA : directory path for low energy EM data
G4LEVELGAMMADATA : directory path for photon evapolation
G4SAIDXSDATA : directory path for nucleon cross section data

For using ROOT libraries

ROOTSYS : root path of the ROOT package

exMPI01

A simple application.

Configuration:

Geometry : chamber / calorimeter
Primary : particle gun (200 MeV electron as default)
Physics List : standard EM

Features:

Particles are transported in a geometry without any scoring.
Learn how to parallelized your G4 session.

exMPI02 (ROOT application)

An example of dosimetry in a water phantom.

Configuration:

Geometry : water phantom
Primary : broad beam (200 MeV proton)
Physics List : FTFP_BERT
Analysis : ROOT histogramming

Features:

Score dose distribution in a water phantom.
Learn how to parallelized your applications.
Create a ROOT file containing histograms/trees in each node.