[petsc-users] src/ksp/ksp/examples/tutorials/ex22.c

[Алексей Рязанов]

Hello!
Help me please to solve my tiny problem with dmmg.

In the example src/ksp/ksp/examples/tutorials/ex22.c, which is discussed on
the 111th page of users manual, we use function
(line 36):
DACreate3d(PETSC_COMM_WORLD,DA_NONPERIODIC,DA_STENCIL_STAR,-3,-3,-3,PETSC_DECIDE,PETSC_DECIDE,PETSC_DECIDE,1,1,0,0,0,&da);
to "*create the DA that stores information about the coarsest grid you wish
to use*".
We can see that negative dimension values (-M, -N, -P) are used  "*to
indicate that it may be set to a different value from the command line with
-da_grid_x <M> -da_grid_y <N> -da_grid_z <P>". *
The question is: when I use -da_grid_ M,N,P options as the size of the
coarsest matrix, what's the size of the finest (most accurate, original
problem) matrix?

I've tried to clear this up, using VecVew on the residual vector and figured
out, that when i'm using M,N,P as input parameters (so define the coarsest
grid as field of M*N*P dots), I get the residual vector of size
(4*M-3)*(4*N-3)*(4*P-3).
Is my result correct?  If yes, could you please explain why it happens in
this way.

Sorry if my question is incorrect. I could mix up everything at all.
Thanks in advance!

-- 
Best regards,
Alexey Ryazanov
______________________________________
Nuclear Safety Institute of Russian Academy of Sciences
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