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testing MAX_FIELD_STEP #229
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I did some tests with different MAX_FIELD_STEP values using jlabce:2.5 container which has gemc 2.9 and geant4.10.7.p03
The field map used has 1cm grid and -FIELD_PROPERTIES="solenoid_CLEOv8, 1*mm, G4ClassicalRK4,linear"
1st test
high energy tracks of chargedgeantino in vacuum shows a few percent difference between default and 1mm as follows, while 100mm,10mm,1mm don't differ much
check details at ifarm by
cd /group/solid/solid_github/JeffersonLab/solid_gemc_test/analysis/field_test
diff solidgem.txt_max1 solidgem.txt_maxdefault
repeat the test by
cp /group/solid/solid_github/JeffersonLab/solid_gemc_test/analysis/field_test/solidgem.gcard ./
cp /group/solid/solid_github/JeffersonLab/solid_gemc_test/analysis/field_test/solidgem__geometry_Original.txt ./
gemc solidgem.gcard -BEAM_P="chargedgeantino,11GeV,12deg,0deg" -BEAM_V="(0,0,-350)cm" -FIELD_DIR="/group/solid/solid_github/JeffersonLab/solid_gemc_test/field" -HALL_FIELD="solenoid_CLEOv8" -FIELD_PROPERTIES="solenoid_CLEOv8, 1mm, G4ClassicalRK4,linear" -MAX_FIELD_STEP=1
more solidgem.txt
2nd test
testing speed of gemc for 1e6 events and SoLID PVDIS full geometry and 1cm3 grid map at different MAX_FIELD_STEP
0-11GeV electrons entering solid at all angles, the speed is 1:1 for MAX_FIELD_STEP default:10mm
11GeV electrons shooting at 40cm LD2 target, the speed is 1:2.5:15 for MAX_FIELD_STEP default:100mm:10mm
my thoughts
MAX_FIELD_STEP in gemc is fLargestAcceptableStep in geant4 (geometry/navigation/src/G4PropagatorInField.cc) whose default 1000m is too large for both high energy particles shown in my test and low energy particles in clas12 test ("moller electrons were jumping un-physically to unshielded areas")
Maybe it's best for our application with 1cm map grid to use MAX_FIELD_STEP 1cm to balance speed and accuracy.
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