[petsc-users] I suggest to create a demo code for the problem of "Get a value from global vector to a local processor"

[leejearl]

Hi all Petscer,
	I have ask helps for some questions. Thanks for the replies
from developer. I have known more about the petsc. I have also sought
helps in the mail lists, and I find that there are many subjects
focused on such a problem. Some subjects are listed as follow


https://lists.mcs.anl.gov/pipermail/petsc-users/2019-January/037425.html
,


https://lists.mcs.anl.gov/mailman/htdig/petsc-users/2015-January/024068.html
,


https://lists.mcs.anl.gov/mailman/htdig/petsc-users/2008-November/003633.html
,


https://lists.mcs.anl.gov/pipermail/petsc-users/2019-January/037436.html

......

The problem can be summarized as
1. Getting the value of vector from other processor
2. How to set the value of ghost cell, the value of the ghost cell
might be as same as a very cell in other processor. 

I think the above problem is very popular. I suffer such a problem when
I want to treat the periodic boundary for the FVM method. After the dm
object is distributed, the donor cell of bound might be in other
processor. Since the donor cell must be matched as a pair correctly,
using the routines DMGlobaltoLocal and DMLocaltoGlobal can not get the
expected results. 

In fact, such a problem is not very difficult for a mpi program. But we
are coding with the petsc, we always think that whether we can
implement more easily.

Whether our developer can create a demo for us to following. I think
such a demo is very useful for user.

Thanks

leejeal