[petsc-users] da_overlap vs width in dmdacreate

[Matthew Knepley]

On Sat, Jun 25, 2016 at 7:18 PM, Xiangdong <epscodes at gmail.com> wrote:

> Maybe my previous email is not clear. What is the relationship between the
> parameter x in DMDASetOverlap and the parameter s in DMDACreate2d? Does x
> need to be smaller than s? Are they completely independent?
>

Yes. The Overlaps are only used in decomposing the DA into small blocks for
things like block GS and NASM.

 Thanks,

    Matt


> PetscErrorCode  DMDASetOverlap(DM da,PetscInt x,PetscInt y,PetscInt z)
>
> PetscErrorCode  DMDACreate2d(MPI_Comm comm,DMBoundaryType
> bx,DMBoundaryType by,DMDAStencilType stencil_type, PetscInt M,PetscInt
> N,PetscInt m,PetscInt n,PetscInt dof,PetscInt s,const PetscInt lx[],const
> PetscInt ly[],DM *da)
>
> Thanks.
>
> Xiangdong
>
>
> On Fri, Jun 24, 2016 at 5:23 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>>
>>    What arguments are you referring to?
>>
>> PetscErrorCode  DMDACreate2d(MPI_Comm comm,DMBoundaryType
>> bx,DMBoundaryType by,DMDAStencilType stencil_type,
>>                           PetscInt M,PetscInt N,PetscInt m,PetscInt
>> n,PetscInt dof,PetscInt s,const PetscInt lx[],const PetscInt ly[],DM *da)
>>
>> the argument s is the stencil width and depends on the finite difference
>> stencil you want to use. There is no da_overlap argument.
>>
>>   Barry
>>
>> > On Jun 24, 2016, at 4:17 PM, Xiangdong <epscodes at gmail.com> wrote:
>> >
>> > Hello everyone,
>> >
>> > I have a quick question. What is the relationship between da_overlap
>> and the width parameter in dmdacreate2d?
>> >
>> > From the examples, it seems that width=1 works with da_overlap=4. Could
>> you please explain the relationship or point me to a reference page?
>> >
>> > Thanks.
>> >
>> > Xiangdong
>>
>>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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