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Forum: Biasing and Scoring
Re: Question Forced-flight biasing: Cumulated weight is null ! (Jayson Vavrek)
Date: 24 Jan, 2017
From: Marc Verderi <Marc Verderi>

Hello Jayson,

The behavior you see is indeed correct, this "forced flight" biasing operation is used in the "forced interaction" scheme la MCNP where one copy of the incoming track is forced to interact in a volume while the other copy is forced to fly through the volume -under a zero weight so that it does not score [in this scheme this would lead to a double counting]- having its weight restored to non-zero (initial weight * weight for free flight) when the volume is crossed. I understand you are interested in having a free flight with the track weight evolving all along the trajectory. Is that correct ? BTW, do you plan to use more recent releases ? (There is no change wrt the free flight, but the underneath biasing code makes the programming of the biasing operations less tricky).

Cheers, Marc

On Tue, 24 Jan 2017 18:57:05 GMT, Jayson Vavrek wrote:

> I'm running geant4-10-00-patch-02 and attempting to use the
> G4BOptnForceFreeFlight() class for forced-flight biasing. While I can
> see in the visualization that my primary gammas are indeed flying freely
> through the volumes to which I've attached the biasing operator, it
> appears that the track weights are not being computed under the hood:
> 
> -------- WWWW ------- G4Exception-START -------- WWWW -------
> *** G4Exception : BIAS.GEN.06
>       issued by :  G4BOptnForceFreeFlight::DenyProcessPostStepDoIt(...)
>  Cumulated weight is null ! 
> *** This is just a warning message. ***
> -------- WWWW -------- G4Exception-END --------- WWWW -------
> 
> In my main.cc I have:
> 
>  physicsList *thePhysics = new physicsList();
> G4GenericBiasingPhysics *theBiasingPhysics = new G4GenericBiasingPhysics();
> theBiasingPhysics->Bias("gamma");
> thePhysics->RegisterPhysics(theBiasingPhysics);
> runManager->SetUserInitialization(thePhysics);
> 
> and I have written my own concrete operator class, forcedFlightOperator
> 
> file forcedFlightOperator.hh:
> 
> #ifndef forcedFlightOperator_hh
> #define forcedFlightOperator_hh 1
> 
> #include "G4VBiasingOperator.hh"
> #include "G4BOptnForceFreeFlight.hh"
> 
> class forcedFlightOperator : public G4VBiasingOperator
> {
> public:
>         forcedFlightOperator();
>         virtual ~forcedFlightOperator();
> 
>         G4BOptnForceFreeFlight *GetForceFreeFlightLaw() {return fForceFreeFlightInteractionLaw;};
> 
> private:
>         G4BOptnForceFreeFlight *fForceFreeFlightInteractionLaw;
> 
>         // used for forced flight
>         virtual G4VBiasingOperation *ProposeOccurenceBiasingOperation(const G4Track*, const G4BiasingProcessInterface* );
> 
>         // unused but required pure virtual functions
>         virtual G4VBiasingOperation *ProposeNonPhysicsBiasingOperation(const G4Track* track, const G4BiasingProcessInterface* callingProcess) { return 0; };
>         virtual G4VBiasingOperation *ProposeFinalStateBiasingOperation(const G4Track*, const G4BiasingProcessInterface* ) { return 0; };
> 
> };
> 
> #endif
> 
> file forcedFlightOperator.cc:
> 
> #include "forcedFlightOperator.hh"
> forcedFlightOperator::forcedFlightOperator() : G4VBiasingOperator("forcedFlightOperator")
> {
>         fForceFreeFlightInteractionLaw = new G4BOptnForceFreeFlight("forcedFlight");
> }
> 
> forcedFlightOperator::~forcedFlightOperator()
> {
>         delete fForceFreeFlightInteractionLaw;
> }
> 
> G4VBiasingOperation *forcedFlightOperator::ProposeOccurenceBiasingOperation(const G4Track*, const G4BiasingProcessInterface*)
> {
>         return fForceFreeFlightInteractionLaw;
> }
> 
> Am I missing something?
> 

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1 None: Re: Forced-flight biasing: Cumulated weight is null !   (Jayson Vavrek - 27 Jan, 2017)
(_ None: Re: Forced-flight biasing: Cumulated weight is null !   (Marc Verderi - 28 Jan, 2017)
(_ None: Re: Forced-flight biasing: Cumulated weight is null !   (Adam Geva - 12 Apr, 2017)
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