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Forum: Geometry
Re: Question Cylindrical Parameterisation Causes Poor Performance (Joseph DeCunha)
Date: 19 Aug, 2016
From: Gabriele Cosmo <Gabriele Cosmo>

Hi Joseph,

parameterisations over phi can definitely be problematic for performance
as they imply recalculation of trigonometric parameters every time the
shape gets changed... no surprise!
If you're application is performance critical, I suggest you to use simple
placements instead for such specific constructs.

Cheers, Gabriele

On Tue, 19 Jul 2016 21:53:42 GMT, Joseph DeCunha wrote:
> Hi there!
> I've just finished coding a cylindrical parameterisation (derived from
> G4VPVParameterisation) class that parameterises along the radius and rho
> axis.
> I'm implementing it in a parallel world in order to score dose. However,
> I've found that compared to other G4VPVParameterisation classes I've
> used the performance overhead is tremendous. For 200 particles my
> simulation time hopped from 4s to 45s.
> I've narrowed the performance hit down to two statements in my
> ComputeDimensions method. My cylinder.SetDeltaPhiAngle and
> cylinder.SetStartPhiAngle statements. When I comment these two
> statements out my performance again returns to an acceptable level.
> The number of parameterisations that I create does have some impact on
> performance -- but I've tried everything from 2500 to 30
> parameterisations and the performance is still very poor.
> I was wondering if this was a known phenomenon or if anyone could help
> push me in the right direction towards what may be behind the problem.
> All the best, and thanks in advance
> Joseph

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