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| 2 | ========================================================= |
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| 3 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP |
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| 4 | ========================================================= |
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| 5 | |
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| 6 | ExampleP01 |
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| 7 | ---------- |
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| 8 | |
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| 9 | General description |
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| 10 | ------------------- |
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| 11 | |
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| 12 | This example shows how to store produced hits in a file using |
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| 13 | the 'reflection' technique for persistency provided by the Reflex tool |
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| 14 | also included in ROOT. The Reflex tool allows to create a dictionary |
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| 15 | for the hit class, making then possible to save hit objects in a .root |
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| 16 | file. The general simulation setup (geometry, physics list, user |
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| 17 | actions, etc...) is taken from ExampleN02. |
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| 18 | |
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| 19 | The provided makefile produces two executables: 'persEx02' and |
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| 20 | 'readHits'. The first one is the actual Geant4 simulation application |
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| 21 | with hits persistency. The second one, is just a simple 'reader' for |
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| 22 | the produced .root file (you need to specify the name of the .root |
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| 23 | file as argument). |
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| 24 | |
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| 25 | |
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| 26 | Building and running the example |
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| 27 | -------------------------------- |
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| 28 | |
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| 29 | Before buidling and/or running the example you need to set the |
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| 30 | following environment variables: |
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| 31 | |
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| 32 | ROOTSYS - ROOT installation directory, it is required to run ROOT |
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| 33 | |
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| 34 | GCCXMLPATH - gccxml binary directory, it is needed by ROOT for the |
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| 35 | dictionary generation |
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| 36 | LD_LIBRARY_PATH - to include the ROOT library path and the path to |
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| 37 | the dictionary library, i.e., for tcsh UNIX shell: |
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| 38 | setenv LD_LIBRARY_PATH ${LD_LIBRARY_PATH}:$ROOTSYS/lib: |
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| 39 | $G4WORKDIR/tmp/$G4SYSTEM/exampleP01 |
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| 40 | |
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| 41 | The present version of the example requires that Geant4 headers are |
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| 42 | installed in a single directory referenced by G4INCLUDE, as the standard |
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| 43 | Geant4 installation procedure allows to do. |
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| 44 | |
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| 45 | Once those variables are set (together with the standard Geant4 setup) |
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| 46 | the example can be build by issueing the 'make' command. The final |
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| 47 | executable file can be found in the usual directory: |
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| 48 | |
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| 49 | $G4WORKDIR/bin/$G4SYSTEM/ |
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| 50 | |
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| 51 | Ten events will be generated and the produced hits will be stored in |
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| 52 | the hits.root file. In addition, the hits will be printed out on the |
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| 53 | screen so one can then compare them with the 'reader' output. |
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| 54 | |
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| 55 | In order to read the persistified hits, a small 'reader' application |
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| 56 | has been implemented. It is build by the same makefile as the example |
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| 57 | executable. It can be run in the following way: |
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| 58 | |
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| 59 | readHits hits.root |
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| 60 | |
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| 61 | where the argument is the name of the file to be read. All the hits |
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| 62 | saved in that file will be then read and printed on the screen. |
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| 63 | |
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| 64 | |
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| 65 | Remark on dictionary generation |
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| 66 | ------------------------------- |
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| 67 | |
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| 68 | The dictionary is generated by ${ROOTSYS}/bin/genreflex |
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| 69 | tool. The header file including headers for all the classes we want to |
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| 70 | generate the dictionary for should be given as argument. Additionally, |
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| 71 | a so called selection file (xml) should be provided (with -s flag) to |
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| 72 | the genreflex tool (see the GNUmakefile). The role of this file is to |
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| 73 | specify which classes we want to generate the dictionary for. The |
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| 74 | selection file for our dictionary is in xml/ directory. Please refer |
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| 75 | to genreflex manual for more details concerning the usage of that |
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| 76 | tool. |
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| 77 | |
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| 78 | Concerning generating dictionary for the Geant4 objects, there are |
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| 79 | also two technical remarks that need to be made here. The gccxml tool |
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| 80 | (version 0.6.0_patch1) requires all the templated classes to be |
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| 81 | explicitely used somewhere in the included header files in order for |
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| 82 | the generation of the dictionary to be possible. For those templated |
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| 83 | classes for which it is not the case, the problem can be very easily |
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| 84 | solved by instaciating them in the headerfile which is given to |
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| 85 | genreflex (see includes/Classes.h) as argument. |
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| 86 | The second remark is that there is an unfortunate clash of names as |
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| 87 | far as G4String class is concerned. The header of G4String class |
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| 88 | defines __G4String which happens to be the name of a variable used |
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| 89 | within the generated dictionary code. The solution for that is to do |
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| 90 | #undef __G4String in include/Classes.h file. |
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| 91 | |
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| 92 | |
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