[petsc-users] PCMG and DMMG

[DU Yongle]

Good morning, everyone:

I have an existing general CFD solver with multigrid implemented. All
functions (initialization, restriction, prolong/interpolation, coarse/fine
grids solver......) are working correctly. Now I am trying to rewrite it
with PETSc. I found that the manual provides very little information about
this and is difficult to follow. I found another lecture notes by Barry
Smith on web, which is:
http://www.mcs.anl.gov/petsc/documentation/tutorials/Columbia04/DDandMultigrid.pdf

However, it is still not clear the difference and connection between PCMG
and DMMG. Some questions are:

1. Should DMMG be used to initialize the coarse grids (and boundary
conditions) before PCMG could be used? If not, how does PCMG know all
information on coarse grids?

2. Due to the customized boundary conditions, indices of the grids,
boundary conditions, grid dimensions on each coarse grid levels are
required for particular computations. How to extract these information in
either DMMG or PCMG? I have not found a function for this purpose. I have
set up all information myself, should I pass these information to the
coarse grid levels to the coarse levels? How and again how to extract these
information?

3. I have the restriction, interpolation, coarse grid solver ...
implemented. How could these be integrated with PETSc functions? It appears
that some functions like PCMGGetSmoother/UP/Down, PCMGSetInterpolation ....
should be used, but how? The online manual simply repeat the name, and
provides no other information.

Thanks a lot.
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