[petsc-users] How/where to update DASetStencilWidth() info

[Matthew Knepley]

On Fri, Jan 6, 2012 at 4:32 PM, Xuefeng Li <li at loyno.edu> wrote:

> On Fri, 6 Jan 2012, Jed Brown wrote:
>
>  On Fri, Jan 6, 2012 at 16:18, Xuefeng Li <li at loyno.edu> wrote:
>>
>>  The stencil width of my DA to a DMMG object is
>>> created to be 1. It is later adjusted using
>>> DASetStencilWidth() to 2.
>>>
>>>
>> You are not supposed to do this.
>>
>> Either call DMDACreate2d() (or whichever dimension you want) or call the
>> sequence
>>
>>  Understand.
>
> However, is there a way to change/adjust the stencil width
> AFTER the DA has been created and set up to a DMMG? Or,
> in general, can we attach different DA objects to a DMMG
> at different times?
>

1) You cannot change this after setting up the DA. Just make another DA,
since
    they are very lightweight.

2) I think structuring new code around DMMG is wrong. It has been removed in
    petsc-dev and is deprecated in 3.2. What are you trying to do?

  Thanks,

    Matt


>   ierr = DMDACreate(comm, da);CHKERRQ(ierr);
>>  ierr = DMDASetDim(*da, 2);CHKERRQ(ierr);
>>  ierr = DMDASetSizes(*da, M, N, 1);CHKERRQ(ierr);
>>  ierr = DMDASetNumProcs(*da, m, n, PETSC_DECIDE);CHKERRQ(ierr);
>>  ierr = DMDASetBoundaryType(*da, bx, by, DMDA_BOUNDARY_NONE);CHKERRQ(**
>> ierr);
>>  ierr = DMDASetDof(*da, dof);CHKERRQ(ierr);
>>  ierr = DMDASetStencilType(*da, stencil_type);CHKERRQ(ierr);
>>  ierr = DMDASetStencilWidth(*da, s);CHKERRQ(ierr);
>>  ierr = DMDASetOwnershipRanges(*da, lx, ly, PETSC_NULL);CHKERRQ(ierr);
>>  ierr = DMSetFromOptions(*da);CHKERRQ(**ierr);
>>  ierr = DMSetUp(*da);CHKERRQ(ierr);
>>
>>
>> I am updating all these functions now to give an error if you call them
>> after DMSetUp().
>>
>>
>>  DAGetInfo() confirmed
>>> that the stencil width is indeed 2. However,
>>> DAGetGhostCorners()/****DAGetCorners() show that
>>> the ghost point width is 1, instead of 2.
>>>
>>>
>>
> Regards,
>
> --Xuefeng Li, (504)865-3340(phone)
>  Like floating clouds, the heart rests easy
>  Like flowing water, the spirit stays free
>       http://www.loyno.edu/~li/home
>  New Orleans, Louisiana (504)865-2051(fax)
>
>


-- 
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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