[petsc-users] Computed Nodes, Ghosted Nodes and Boundary Nodes

[Matthew Knepley]

On Thu, Aug 25, 2011 at 11:24 PM, Alan Wei <zhenglun.wei at gmail.com> wrote:

> Dear all,
>     I hope you had a nice day.
>     I have a little bit confusion on src/ksp/ksp/example/tutorial/ex29.c,
> which is solving a Poisson equation. The key problem is that I confused
> what is the ghosted node, computed nodes and boundary nodes.
>     1) For example, if the mesh has 20 * 50 grid on x-, y- direction. For
> my understanding, nodes of i = 0, i = 19, j = 0, j = 49 are all boundary
> nodes and others are computation nodes. If a Dirichlet boundary condition
> is applied in node j = 49, then the value of node j = 49 should be a
> constant; while, if a Neumann boundary condition is applied in j = 49,
> then change rate from node j = 48 to j = 49 should be a constant.
>

Fine.


>     2) Moreover, If this code is ran with 2 processes, which 2 on
> y-direction. This leads a 20 * 25 mesh for each nodes, then the ghost nodes
> is created around the local mesh in order to pass data back and forth with
> the other node. Is that correct? However, what is the ghost nodes coordinate
> value and index?
>

For proc0, the ghost nodes would be j = 25, and for proc 1 j = 24. However,
you should not need to worry about this.

   Matt


> Thanks in advance,
> Alan
>



-- 
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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