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Forum: Event and Track Management
Re: Question stepping error (Jeremy McCormick)
Date: 05 Jul, 2016
From: Gabriele Cosmo <Gabriele Cosmo>

Hi Jeremy,

this error indicates a problem of convergence in field integration, which can
happen. This exception (and proper handling for such relatively rare cases) has
been relaxed and turned to a warning in release 10.2. So, you may want to upgrade
to the latest release!

Cheers, Gabriele

-----------------
On Wed, 06 Jul 2016 00:55:37 GMT, Jeremy McCormick wrote:
> Hello,
> 
> I'm getting the following error in my simulation after many thousands of
> events run successfully....
> 
> -------- WWWW ------- G4Exception-START -------- WWWW -------
> *** G4Exception : GeomNav1002
>       issued by : G4MultiLevelLocator::EstimateIntersectionPoint()
> Many substeps while trying to locate intersection.
>           Undertaken length: 295287 - Needed: 3972 substeps.
>           Warning level = 1000 and maximum substeps = 10000
> *** This is just a warning message. ***
> -------- WWWW -------- G4Exception-END --------- WWWW -------
> 
> ERROR - G4MultiLevelLocator::EstimateIntersectionPoint()
>         Start and end-point of requested Step:
> Start         0 -62.141037 -242.15386  128.69337 -0.2353  0.2033 -0.9504       0         0         9.22 Init/NotKnown
>        Current Position  and  Direction
> Step#       s        X(mm)      Y(mm)      Z(mm)    N_x     N_y     N_z   Delta|N|   StepLen  StartSafety   PhsStep
>    0  286581.25 -67483.449  58031.474 -272244.88 -0.2353  0.2033 -0.9504       0  2.87e+05         9.22 Init/NotKnown
>         Start and end-point of current Sub-Step:
> 
> -------- EEEE ------- G4Exception-START -------- EEEE -------
> *** G4Exception : GeomNav0003
>       issued by : G4MultiLevelLocator::EstimateIntersectionPoint()
> Too many substeps!
>          Convergence is requiring too many substeps: 10002
>           Abandoning effort to intersect.
>           Found intersection = 0
>           Intersection exists = 1
>         Undertaken only length: 1190 out of 286581 required.
>         Remaining length = 285391
> *** Fatal Exception *** core dump ***
> -------- EEEE -------- G4Exception-END --------- EEEE -------
> 
> This is with the geant4-10-01-patch-02 version (I can update that to the
> current release if it would make any difference).
> 
> I ran the geometry overlap check and it reported no issues at all.
> 
> I assume it is a low energy secondary that is failing to step through a
> B-field.
> 
> Is there a setting that I can enable which would cause G4 to simply kill
> the stuck track instead of causing a crash? Or is there some other way
> to debug/fix this?
> 
> Thanks.
> 
> --Jeremy

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