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Subject: Re: [PIConGPU-Users] Grid specification.
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Date: Mon, 23 May 2016 11:11:43 +0200
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Dear Danila,

thank you for using PIConGPU.
The grid sizes needs to be a multiple of the supercell size 
(memory.param) per gpu. The default supercell size is 8x8x4 (direction X 
x Y x Z).
If you run your example with `-d 2 8 2` than a working configuration is 
`-g 256 3712 256`.
Please keep in mind if moving window `-m` is enabled the real simulation 
volume is reduced by one gpu [1] in Y (laser propagation) direction.

best,

René

[1] 
https://github.com/ComputationalRadiationPhysics/picongpu/wiki/PIConGPU-domain-definitions#moving-window

On 23.05.2016 10:58, Khikhlukha Danila wrote:
> Hi all,
> I have some problems trying to specify my computational grid in a
> current realieaze version.
> I'm not sure if I'm doing everything right. Could you please take a look?
>
> 1. In my simulation I was trying to setup a moving simulation box with
> dimensions 100x100x100 um. I also was trying to
> set the resolution in propagation direction much higher, so I specified
> the number of cells like: "TBG_gridSize="-g 250 3750 250""
> and TBG_movingWindow="-m"
>
> 2. In a gridConfig.param file I specified computational cell digestions
> to fit the simulation box size  CELL_WIDTH_SI = 4.0e-7,
> CELL_HEIGHT_SI = 2.6666e-8 and CELL_DEPTH_SI = CELL_WIDTH_SI. I also
> specifed the time step to match CFL condition
> DELTA_T_SI = 8.8558e-17
>
> 3. While compiling I got a static assert error about CFL condition being
> violeted, whihc is a bit strange, since the numbers above
> give Courant number = 0.999981852222.
>
> 4. Considering some possible round-off errors I decided to increase the
> time step to make Courant number lower.
> So I changed it to DELTA_T_SI = 8.855e-17 and it helped to compile.
>
> 5. Trying run it I recieved another assert error:
>  > [1,0]<stderr>:picongpu:
> /home/danila/tools/picongpu/src/picongpu/include/simulationControl/MySimulation.hpp:484:
>  >void
> picongpu::MySimulation::checkGridConfiguration(PMacc::DataSpace<DIM>,
> PMacc::GridLayout<DIM>) [with unsigned int DIM = 3u]: Assertion
> `globalGridSize[i] % MappingDesc::SuperCellSize::toRT()[i] == 0' failed.
> I'm not sure I'm clear about it. What is a SuperCellSize?... I've
> checked the source code and found a message that this check
> is redundant. However further manipulations in the code unfortunately
> are not very clear to me...
>
> Could you please take a look if I'm doing something wrong?
>
> Best regards,
> Danila.

-- 
René Widera
Abteilung Laser-Teilchenbeschleunigung (FWKT)
Helmholtz-Zentrum Dresden-Rossendorf
Tel: +49 (0351) 260 3543
r.widera@hzdr.de
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