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

[Alan Wei]

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.
    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?

Thanks in advance,
Alan
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