Gabriele Cosmo
150 lines
6.0 KiB
Plaintext
150 lines
6.0 KiB
Plaintext
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Examples for event biasing
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--------------------------
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This directory includes example applications to demonstrate the usage of
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different biasing techniques supported in Geant4, or possible from the
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user applications.
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General remark to biasing
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-------------------------
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The tools provided for importance sampling (or geometrical splitting and
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Russian roulette) require the user to have a good understanding of the
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physics in the problem. This is because the user has to decide which
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particle types have to be biased, define the regions (physical volumes,
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replicas) and assign importances to that regions. If this is not done
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properly it can not be expected that the results describe a real
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experiment. The examples given here only demonstrate how to use the tools
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technically. They don't intend to produce physical correct results.
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General remark to scoring
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-------------------------
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A interface G4VScorer is provided for the user. The user may create his
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own class to perform the desired scoring. The user defined class
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therefore should inherit from the interface G4VScorer.
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An example of an implementation of a scorer is G4Scorer
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which may be found in source/event.
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The scoring in these examples is done with a G4Scorer.
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Importance sampling and scoring does not support all options of the
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Geant4 geometry. It only supports physical volumes and simple replicas.
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To identify a physical volume (or replica) objects of the class
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G4GeometryCell are used. Scoring is done according to these
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cells and importance values may be assigned to them.
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When scoring is done in a "scoring" or in a "importance" geometry
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special action has to be taken to prevent counting of
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"collisions" with boundaries of the tracking geometry as interactions.
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This is differently handled when scoring is done in the tracking geometry.
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--> G4GeometryCell must not share boundaries with the world volume! <--
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Known problems
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--------------
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In the following scenario it can happen that a particle is not
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biased and it's weight is therefore not changed even if it crosses
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a boundary where biasing should happen.
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The importance sampling creates particles on boundaries
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between volumes. If the GPIL method of a physical process returns
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0 as step length for a particle on a boundary and if the PostStepDoIt of
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that process changes the direction of the particle to go back in the
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former volume the biasing won't be invoked.
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This will produce particles with weights that do not correspondent to the
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importance of the current volumes.
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Further information:
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--------------------
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Short description of importance sampling and scoring:
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http://dressel.home.cern.ch/dressel/biasscore/Sampling.html
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Example B01
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===========
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The example uses importance sampling and scoring. Importance values are
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defined according to the mass geometry. Scoring is also done in according
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to the mass geometry.
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Example B02
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===========
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This example uses a parallel geometry to define G4GeometryCell objects
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for scoring and importance sampling. In addition it customizes
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the scoring. In this example one scorer creates a histogram.
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Compiling and running
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---------------------
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To compile this example you need AIDA 3.0 installed. To link
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and run it you need a AIDA compliant analysis package. The
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GNUmakefile of this example shows how to use Anaphe as analysis
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package.
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The following list shows what to do if you are at CERN using rehat61
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and gcc-2.95.2:
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use the shell /bin/sh
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1) set the following variables (for example):
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ANAPHETOP=/afs/cern.ch/sw/lhcxx
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(or if installed in opt: /opt/Anaphe/5.0.1)
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AIDA_DIR=/afs/cern.ch/sw/contrib/AIDA/3.0/src/cpp
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(or if installed in opt: /opt/AIDA/3.0.0/3.0.0/AIDA/3.0/src/cpp)
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export ANAPHETOP AIDA_DIR
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2) Source the script:
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. $ANAPHETOP/share/LHCXX/5.0.1/scripts/setupAnaphe
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3) and add to lirary path the following directories:
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LD_LIBRARY_PATH=${LD_LIBRARY_PATH}:${G4WORKDIR}/lib/${G4SYSTEM}:${G4WORKDIR}/tmp/${G4SYSTEM}/exampleB02
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Now you should be able to run gmake and to run exampleB02.
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The example stores the plot in the file b02.hbook.
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To look at the histogram using lizard you also may use Anaphe 5.0.1
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http://anaphe.web.cern.ch/anaphe/index2.html.
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Files in B02:
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B02plot.py: a simple script that may be executed from a lizzard session
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to show the plot created by running the exampleB02.
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Example B03
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===========
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This example uses Geant4 and in particular importance sampling and
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scoring through python. It also creates a histogram.
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Compiling and running
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---------------------
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To compile and run this example you need a python2.2 installation
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see http://www.python.org.
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Please set the environment variable "PYTHON_DIR" to your python2.2
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installation e.g:
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using afs:
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to /afs/cern.ch/sw/lhcxx/specific/redhat61/gcc-2.95.2/PublicDomainPackages/2.0.0
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or if Anaphe is installed in opt /opt/Anaphe/5.0.1/specific/redhat72/gcc-2.95.2/PublicDomainPackages/2.0.0.
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Please add to your environment variables
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setenv LD_LIBRARY_PATH ${LD_LIBRARY_PATH}:${G4WORKDIR}/lib/${G4SYSTEM}:${G4WORKDIR}/tmp/${G4SYSTEM}/exampleB03
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and setenv PYTHONPATH $LD_LIBRARY_PATH.
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You may run gmake now.
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You should be able to execute the file B03RunApplication.py from your
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shell now.
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If you have Anaphe 5.0.1 installed you may also execute the file
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B03RunApplication.py from a lizard session. This will create a
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histogram. Therefore you may follow the steps 1 and two
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in the above exampleB02.
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See http://anaphe.web.cern.ch/anaphe/index2.html.
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Files in B03;
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env.csh: Is an example script to set the environment. It should work
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if you are at CERN and if you are on a redhat6.1 system.
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buildit.sh: You don't need to use this file. Only if you want to
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make changes to the python interface defined in B03App.i you may need
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to use it.
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B03Application.py: Is a example class utilizing importance sampling
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and scoring using python.
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B03RunApplication.py: Is a python script running the example.
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It may be executed from the shell or in a python or lizard
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session. In case it is executed from lizard it creates a plot
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with a histogram.
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B03App.py: Is created by swig using the buildit.sh script.
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