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Re: Question Stepsize limitation (I Cornelius)
Date: 19 Mar, 2004
From: michel maire <michel maire>

 In Physics Reference Manual, item Computing the energy loss :

 Stepsize Limit Due to Continuous Energy Loss 

 "Continuous energy loss imposes a limit on the stepsize because of the energy dependence of the cross sections. It is generally assumed in MC programs
 that the particle cross sections are approximately constant along a step, i.e. the step size should be small enough that the change in cross section, from
 the beginning of the step to the end, is also small. In principle one must use very small steps in order to insure an accurate simulation, however the
 computing time increases as the stepsize decreases. A good compromise is to limit the stepsize by not allowing the stopping range of the particle to
 decrease by more than 20 % during the step. This condition works well for particles with kinetic energies , but for lower energies it gives very
 short stepsizes. 

 To cure this problem a lower limit on the stepsize was introduced. There is a natural choice for this limit: the stepsize cannot be smaller than the range
 cut parameter of the program. The stepsize limit varies smoothly with decreasing energy from the value given by the condition  to the
 lowest possible value range cut. These are the default step limitation parameters; they can be overwritten using the UI command
 ``/process/eLoss/StepFunction 0.2 1 mm'', for example." 

 This mechanism is handled automatically by G4VEnergyLossProcess.

 See also the plot in :
 http://wwwasd.web.cern.ch/wwwasd/geant4/reports/gallery/electromagnetic/stepping/stepping.html 

 The 2 parameters of the function which control smoothly the limitation
 of the step size can be set with the command /process/eLoss/StepFunction

 See examples/extended/electromagnetic/TestEm1, for instance the macro
 run01.mac

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1 None: Re: Stepsize limitation   (I Cornelius - 22 Mar, 2004)
(_ None: Re: Stepsize limitation   (Vladimir IVANTCHENKO - 22 Mar, 2004)
(_ None: Re: Stepsize limitation   (I Cornelius - 22 Mar, 2004)
1 None: Re: Stepsize limitation   (Vladimir IVANTCHENKO - 22 Mar, 2004)
1 Question: Re: Stepsize limitation   (Dipanwita Banerjee - 14 Aug, 2013)
... 1 Message(s)
2 None: Re: Stepsize limitation   (Alexander Kish - 13 Apr, 2007)
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