[petsc-users] [petsc-maint] Question about DMDA BOUNDARY_CONDITION set

[Barry Smith]

   I can cook up a simple example that communicates the needed ghost values for your boundary conditions.  It may take a day or two.

    Are you using a five point stencil or a nine point stencil (the nine point stencil seems "weird" for that very corner point)?


  Barry

> On Mar 21, 2017, at 8:46 AM, Wenbo Zhao <zhaowenbo.npic at gmail.com> wrote:
> 
> Matt,
> 
> Thanks.
> 
> I want to solve neutron diffusion equations using finite difference method and PETSc.
> This rotation boundary condition is very common in my cases.
> Though the mesh consists of  ~ 10 Miliion structured hexahedron cells, the mesh is simple and could be discribed by three vectors about x, y and z axis.
> It is appropriate for DMDA except boundary condition. 
> 
> I wanted to make mesh partition like DMDA by hand. Then I need to create matrix and vector and assemble matrix, and et al. I thought it was an easy work.
> As you say, it's not.
> 
> As a newer, I can use DACreate2d to begin. It's OK.
> But finally, it does need this optimization.
> 
> Though I read the manual about the vector and matrix, I am not clear about the basic idea behind the code.
> How can I create a matrix and vector as my mesh partition and create the map between the nature ordering and the PETSc ordering in global vector?
> How does vector communicate in the operation of matrix multi vector? Does it achieved automatically?
> 
> BETS,
> 
> Wenbo
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