PCNN preconditioner and setting the interface

[Barry Smith]

On Mar 24, 2009, at 8:45 AM, Andreas Grassl wrote:

> Hello,
>
> I'm working with a FE-Software where I get out the element stiffness
> matrices and the element-node correspondency to setup the stiffness
> matrix for solving with PETSc.
>
> I'm currently fighting with the interface definition. My
> LocalToGlobalMapping for test-purposes was the "identity"-IS, but I
> guess this is far from the optimum, because nowhere is defined a node
> set of interface nodes.
>
> How do I declare the interface? Is it simply a reordering of the  
> nodes,
> the inner nodes are numbered first and the interface nodes last?

     The order that you list the nodes is not important; the interface  
ones don't have to be listed at the end.

    Here's the deal. Over all the processors you have to have a single  
GLOBAL numbering of the
nodes. The first process starts with 0 and each process starts off  
with one more than then previous process had.
For example with consider two elements, say the first process owns the  
first element and the second process the
second.

   global numbering

                   2
                  / |\
                /   |  \
             /      |     \
           /        |       \
       0    ------------   3
                   1

   local numbering process 0


                   2
                  / |
                /   |
             /      |
           /        |
       0    ------
                   1     local to global numbering is 0 1 2


    local numbering process 1


                   1
                   |\
                   |  \
                   |     \
                   |       \
                   ----    2
                   0                 local to global numbering is 1    
2   3

BUT the local numbering is arbitrary, for example you could order the  
local nodes on process zero with



                   0
                  / |
                /   |
             /      |
           /        |
       2    ------
                   1     then the local to global numbering is 2 1 0  
on process 0













>
>
> Thank you in advance
>
> ando
>
> -- 
> /"\                               Grassl Andreas
> \ /    ASCII Ribbon Campaign      Uni Innsbruck Institut f. Mathematik
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> / \                               +43 (0)512 507 6091
>
>