[petsc-users] AOApplicationToPetscIS

[Hui Zhang]

On Apr 15, 2013, at 5:55 PM, Matthew Knepley wrote:

> On Mon, Apr 15, 2013 at 10:52 AM, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
> I'm implementing a domain decomposition preconditioner.  The dof is ordered by myapp and using AO (and LocalToGlobalMapping for assembly) to map to petsc ordering.
> The task I'm doing is building VecScatter's from subdomains to the global domain.  So my program is
> 
> I do not understand why you would need AOs for this. They are for global reordering, whereas you seem to only
> need a local mapping here.

To use 

	ISLocalToGlobalMappingCreate(MPI_Comm cm,PetscInt n,const PetscInt indices[],PetscCopyMode mode,ISLocalToGlobalMapping *mapping)

In the manual page, it says "Not Collective, but communicator may have more than one process".  What is the purpose of using a communicator other than SELF_COMM? Will the input indices[] be gathered in the communicator 'cm'?

Now I understand why AOCreateBasic is not scalable.  But I still need to use it in the beginning for construction of LocalToGlobalMapping.  How did you implement the LocalToGlobalMapping for element-based decomposition?  Did you avoid using any AO?

> 
>    Matt
>  
> Step 1.  I can map subdomain petsc ordering to subdomain natural ordering.
> 
> Step 2.  I can also map subdomain natural ordering to global domain natural ordering.
> 
> Step 3.  I have an AO for mapping global domain natural ordering to petsc ordering.
> 
> Since each subdomain is defined on a sub-communicator of the communicator of the global domain.  My question is for
> 
> AOApplicationToPetscIS(AO ao,IS is)
> 
> can ao and is have different communicators?  Will my program be bad for large problems?  How would you do it?
> 
> 
> 
> -- 
> 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