[Users] periodic boundary condition

[Erik Schnetter]

On Apr 3, 2008, at 21:25:44, #NGUYEN CONG TRI# wrote:
> Dear all,
>
> I'm sorry but it's not very clear for me how PUGH actually implement  
> periodic boundary conditions. For example, I want to specify  
> driver::periodic_x = "yes" and driver::global_nx = 65,  
> driver::ghost_size = 1, then during partition will the driver  
> automatically augment 2 appropriate ghost cells and my physical  
> domain is still [0, 64] or it will use points 0 and 64 as ghost  
> cells and my physical domain is only [1,63] ? I believe the latter  
> is used in reflection symmetry but I'm not sure about the periodic  
> boundary condition.

Tri,

In your case, the physical domain would be [1, 63].

Internally in PUGH, periodic boundaries are treated in the same way as  
inter-processor boundaries, and no special explicit symmetry  
operations are required as would be the case for reflection symmetry.   
This means among other things that the additional points which  
implement periodicity are not output, in the same way that inter- 
processor ghost zones are not output.  This can be slightly confusing,  
since one may think that these points are missing.

When you use periodic boundaries, you have to be careful about the  
size of the simulation domain that you specify.  If you want to set up  
a domain of extent [0; 1) with a grid spacing of 0.1 and one ghost  
zone, then you need to specify xmin=-0.1, xmax=+1.0, and you need to  
choose 12 grid points.

The thorn CactusExamples/WaveToy1DF77 has an example with a 1D wave  
equation.  The example is not quite ideal, since it specifies 101 grid  
points which leads to 99 interior points, or a physical domain of size  
0.99 instead of 1.0.

-erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>   http://www.cct.lsu.edu/~eschnett/

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