Problem 807 - NAN at G4BraggModel
Summary: NAN at G4BraggModel
Status: RESOLVED FIXED
Alias: None
Product: Geant4
Classification: Unclassified
Component: processes/electromagnetic (show other problems)
Version: 7.1
Hardware: PC Linux
: P2 normal
Assignee: Michel.Maire
URL:
Depends on:
Blocks:
 
Reported: 2005-10-23 04:00 CEST by nanjo
Modified: 2005-10-24 03:44 CEST (History)
1 user (show)

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Description nanjo 2005-10-23 04:00:22 CEST 
Dear GEANT4 developer,

In a method, G4BraggModel::SampleSecondaries,
a negative value can be passed to sqrt()
at the line number of 213 in G4BraggModel.cc.

213   G4double sint = sqrt(1.0 - cost*cost);

It makes a new momentum direction of a particle after the step NAN.

For my case,
the tracked particle is Ar40[0,0] in the standard air,
and its momentum vector is (116,258,-25.3),
and 1.0-cost*cost = -6.85e-13.

Is it due to the precision of the calculation?

Anyway, I think it can be fixed by
adding some check against the negative value before sqrt().

Could you fix this problem?

Best Regards,
Hajime
--------------------------------------------------
High Energy Physics Group, Department of Physics,
Kyoto University
Hajime Nanjo
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Comment 1 Vladimir.Ivantchenko 2005-10-24 03:44:59 CEST 
The bug have been fixed and the fix will be available with Geant4 7.1 patch 01