[petsc-users] Is there easy to update the ghost value in the vector created using DMCreatLocalVector?

[leejearl]

Hi Matt，	I think it is not a bug. DMGlobaltoLocal works well.
Maybe I have not explain my problem clearly.I will detail it
tomorrow.       Thanks，leejearl

On Wed, 2019-01-16 at 09:15 -0500, Matthew Knepley wrote:
> On Wed, Jan 16, 2019 at 8:52 AM leejearl <leejearl at mail.nwpu.edu.cn>
> wrote:
> > Hi Matt,
> > 	Thanks for you reply.  If I use  DMGlobalToLocal() to update
> > the local vector from global vector.
> > The value of cStart<=c<cEndinterior is ok. But the value of
> > cEndInterior<=c<cEnd is not the right value.
> > 	I do not know whether it has something to do with the
> > DMGlobalToLocal().  My problem is as follow.
> > After the mesh is distributed , the cells and ghost cells (local
> > vector) look like
> 
> Hmm, that sounds like a bug, but I have to think a little bit. I
> don't see how TS ex11 can be working in parallelif overlapping cells
> are not being updated. We should make a small example so that we are
> certainly comparing thesame things.
>   Thanks,
>     Matt 
> > processor 0: 0, 1, 2, 3, 4 (cell 4 is the ghost cell)
> > processor 1: 0, 1, 2, 3, 4 (cell 4 is the ghost cell)
> > 
> > The value of cell 4 in "processor 0" is same as the value of  cell
> > 0 in "processor 1". The value of cell 0 in  "processor 1" has
> > been set in the global vector. I should copy  the corresponding
> > global value of cell 0 in  "processor 1"  to cell 4 in  "processor
> > 0".
> > 
> > This is my problem. I want to know how to implement it easily. Can
> > you give me some advices?
> > 
> > Thanks
> > 
> > leejearl
> > 
> > 
> > On Wed, 2019-01-16 at 08:07 -0500, Matthew Knepley wrote:
> > > On Tue, Jan 15, 2019 at 8:34 PM leejearl via petsc-users <
> > > petsc-users at mcs.anl.gov> wrote:
> > > > Hi all Petscer,
> > > > 
> > > > 
> > > > 
> > > > I have a question about how to update the ghost value in the
> > > > vector.
> > > > 
> > > > The prolblem is as follow.
> > > > 
> > > > 
> > > > 
> > > > 1. A dmplex dm object is created using DMPlexCreateFromFile
> > > > 
> > > > 2. The dm is distributed using DMPlexDistribute, and the
> > > > overlap is set
> > > > 
> > > > as 1.
> > > > 
> > > > 3. The ghosted dm is constructed by DMConstructGhostCells.
> > > > 
> > > > 4. A global Vector X and a local vector localX are created by
> > > > 
> > > > DMCreateGlobalVector and DMCreateLocalVector
> > > > 
> > > > 
> > > > 
> > > > Now, the problem is that the ghost value are needed in the
> > > > computation
> > > > 
> > > > using local vector localX. and the ghost value must be update
> > > > from the
> > > > 
> > > > global vector. 
> > > > 
> > > > 
> > > > 
> > > > For example, gCellId is the index of ghost cell in the local
> > > > vector
> > > > 
> > > > localX of process 0, and cellId is the index of cell in the
> > > > global
> > > > 
> > > > vector of process 1. I must update the data of cellId to
> > > > gCellId. How
> > > > 
> > > > can I do it easily?
> > > > 
> > > > 
> > > > 
> > > > I can implement it use the PetscSFBcastBegin/PetscSFBcastEnd.
> > > > Is there
> > > > 
> > > > other simple way to do it?
> > > 
> > > Doesn't DMGlobalToLocal() work?
> > >   Thanks,
> > >     Matt 
> > > > Any helps are appreciated.
> > > > 
> > > > 
> > > > 
> > > > Thanks.
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > leejearl
> > > > 
> > > > 
> > > > 
> > > 
> > > 
> 
> 
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