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Forum: Fields: Magnetic and Otherwise
Re: Sad the proper time goes back (Olivier Dadoun)
Re: Ok Re: the proper time goes back (Olivier Dadoun)
Date: 17 Sep, 2009
From: Gumplinger Peter <Gumplinger Peter>

Dear Oliver,

> I have followed the recommendation gave by

> Peter Gumplinger http://tinyurl.com/nfpk7t

Thanks for bringing this to my/users' attention. The code in the above forum link is still not entierly correct; it would be for a localized pure magnetic field but for EM-fields we need:

   G4int nvar = 8;  // To integrate time & energy 
                    //    in addition to position, momentum

and the correct code for EM-fields should read:

    G4int nvar = 8;
    fStepper = new G4ClassicalRK4( fEquation, nvar );

for the default in the G4ClassicalRK4 constructor is nvar=6 and hence tailored to pure mag. fields.

you can then subsequently use:

    fIntgrDriver = new G4MagInt_Driver(fMinStep, 
                                     fStepper, 
                                     fStepper->GetNumberOfVariables() );

This should be the right approach rather than just:

    fIntgrDriver = new G4MagInt_Driver(fMinStep, 
                                     fStepper, 
                                     8);

Please, also see the code fragment (Example 4.12) in the Application Developers Guide:

http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/ForApplicationDeveloper/html/ch04s03.html#sect.EMField.Pract

Regards, Peter

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