Gabriele Cosmo
93 lines
3.9 KiB
Plaintext
93 lines
3.9 KiB
Plaintext
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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ExampleP01
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----------
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General description
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-------------------
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This example shows how to store produced hits in a file using
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the 'reflection' technique for persistency provided by the Reflex tool
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also included in ROOT. The Reflex tool allows to create a dictionary
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for the hit class, making then possible to save hit objects in a .root
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file. The general simulation setup (geometry, physics list, user
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actions, etc...) is taken from ExampleN02.
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The provided makefile produces two executables: 'persEx02' and
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'readHits'. The first one is the actual Geant4 simulation application
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with hits persistency. The second one, is just a simple 'reader' for
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the produced .root file (you need to specify the name of the .root
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file as argument).
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Building and running the example
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--------------------------------
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Before buidling and/or running the example you need to set the
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following environment variables:
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ROOTSYS - ROOT installation directory, it is required to run ROOT
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GCCXMLPATH - gccxml binary directory, it is needed by ROOT for the
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dictionary generation
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LD_LIBRARY_PATH - to include the ROOT library path and the path to
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the dictionary library, i.e., for tcsh UNIX shell:
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setenv LD_LIBRARY_PATH ${LD_LIBRARY_PATH}:$ROOTSYS/lib:
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$G4WORKDIR/tmp/$G4SYSTEM/exampleP01
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The present version of the example requires that Geant4 headers are
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installed in a single directory referenced by G4INCLUDE, as the standard
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Geant4 installation procedure allows to do.
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Once those variables are set (together with the standard Geant4 setup)
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the example can be build by issueing the 'make' command. The final
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executable file can be found in the usual directory:
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$G4WORKDIR/bin/$G4SYSTEM/
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Ten events will be generated and the produced hits will be stored in
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the hits.root file. In addition, the hits will be printed out on the
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screen so one can then compare them with the 'reader' output.
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In order to read the persistified hits, a small 'reader' application
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has been implemented. It is build by the same makefile as the example
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executable. It can be run in the following way:
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readHits hits.root
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where the argument is the name of the file to be read. All the hits
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saved in that file will be then read and printed on the screen.
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Remark on dictionary generation
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-------------------------------
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The dictionary is generated by ${ROOTSYS}/bin/genreflex
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tool. The header file including headers for all the classes we want to
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generate the dictionary for should be given as argument. Additionally,
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a so called selection file (xml) should be provided (with -s flag) to
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the genreflex tool (see the GNUmakefile). The role of this file is to
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specify which classes we want to generate the dictionary for. The
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selection file for our dictionary is in xml/ directory. Please refer
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to genreflex manual for more details concerning the usage of that
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tool.
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Concerning generating dictionary for the Geant4 objects, there are
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also two technical remarks that need to be made here. The gccxml tool
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(version 0.6.0_patch1) requires all the templated classes to be
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explicitely used somewhere in the included header files in order for
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the generation of the dictionary to be possible. For those templated
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classes for which it is not the case, the problem can be very easily
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solved by instaciating them in the headerfile which is given to
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genreflex (see includes/Classes.h) as argument.
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The second remark is that there is an unfortunate clash of names as
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far as G4String class is concerned. The header of G4String class
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defines __G4String which happens to be the name of a variable used
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within the generated dictionary code. The solution for that is to do
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#undef __G4String in include/Classes.h file.
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