[petsc-users] DMDACreateSection

[Hui Zhang]

One more question: why does not DMDACreateSection include d.o.f on edges in 3D?
I think it is very useful for the sub-structuring methods on structured meshes.
For example, the BPS preconditioner, the wire-basket preconditioner on a structured
coarse mesh (one subdomain per element) involve interface d.o.f. on faces, edges and
vertices.

On Jan 22, 2013, at 10:34 AM, Hui Zhang wrote:

> Hi petsc-group,
> 
> if I want to map a structured mesh onto processors by partition of mesh **elements**,
> can I use DMDACreate3d -> DMDACreateSection, then DMDACreateLocal(Global)Vector to 
> give me the vector corresponding to my Q1-element d.o.f.?
> 
> I ask because according to the manual, the usual use of DMDA is only for partition of 
> **nodes** to processors and the local vector is not corresponding to partition of elements.
> For example, consider the Q1 element on the 1D mesh, (numbers for nodes)
> 
> 1--2--3--4--5
> 
> Given two processors, I want the local vector after partition to reside on the partitioned mesh
> 
> 1--2--3   3--4--5  
> proc 0    proc 1
> 
> The global value of d.o.f at the node 3 may be managed by proc 1, and proc 0 only ghosts it.
> If it is the case, proc1 does not ghost any value.
> 
> This is different from the usual DMDA for finite difference stencils, in which the ghosting
> is symmetric, i.e. both proc0 and proc1 will ghost some values.
> 
> Thanks in advance!
> 
> 
> 
>