[petsc-users] GMRES -> PCMG -> PCASM pre- post- smoother

[Aulisa, Eugenio]

Hi,

I am solving an iteration of

GMRES -> PCMG -> PCASM 

where I build my particular ASM domain decomposition.

In setting the PCMG I would like at each level 
to use the same pre- and post-smoother
and for this reason I am using 
...
PCMGGetSmoother ( pcMG, level , &subksp );

to extract and set at each level the ksp object.

In setting PCASM then I use
...
KSPGetPC ( subksp, &subpc );
PCSetType ( subpc, PCASM );
...
and then set my own decomposition
...
PCASMSetLocalSubdomains(subpc,_is_loc_idx.size(),&_is_ovl[0],&_is_loc[0]);
...

Now everything compiles, and runs with no memory leakage, 
but I do not get the expected convergence.

When I checked the output of -ksp_view, I saw something that puzzled me:
at each level >0, while in the MG pre-smoother the ASM domain decomposition
is the one that I set, for example with 4 processes  I get

>>>>>>>>>>>>>>>>>>>
...
 Down solver (pre-smoother) on level 2 -------------------------------
    KSP Object:    (level-2)     4 MPI processes
      type: gmres
        GMRES: restart=30, using Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement
        GMRES: happy breakdown tolerance 1e-30
      maximum iterations=1
      using preconditioner applied to right hand side for initial guess
      tolerances:  relative=1e-12, absolute=1e-20, divergence=1e+50
      left preconditioning
      using nonzero initial guess
      using NONE norm type for convergence test
    PC Object:    (level-2)     4 MPI processes
      type: asm
        Additive Schwarz: total subdomain blocks = 198, amount of overlap = 0
        Additive Schwarz: restriction/interpolation type - RESTRICT
        [0] number of local blocks = 52
        [1] number of local blocks = 48
        [2] number of local blocks = 48
        [3] number of local blocks = 50
        Local solve info for each block is in the following KSP and PC objects:
        - - - - - - - - - - - - - - - - - -
...
>>>>>>>>>>>


in the post-smoother I have the default ASM  decomposition with overlapping 1:


>>>>>>>>>>>
...
 Up solver (post-smoother) on level 2 -------------------------------
    KSP Object:    (level-2)     4 MPI processes
      type: gmres
        GMRES: restart=30, using Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement
        GMRES: happy breakdown tolerance 1e-30
      maximum iterations=2
      tolerances:  relative=1e-12, absolute=1e-20, divergence=1e+50
      left preconditioning
      using nonzero initial guess
      using NONE norm type for convergence test
    PC Object:    (level-2)     4 MPI processes
      type: asm
        Additive Schwarz: total subdomain blocks = 4, amount of overlap = 1
        Additive Schwarz: restriction/interpolation type - RESTRICT
        Local solve is same for all blocks, in the following KSP and PC objects:
      KSP Object:      (level-2sub_)       1 MPI processes
        type: preonly
        maximum iterations=10000, initial guess is zero
        tolerances:  relative=1e-05, absolute=1e-50, divergence=10000
        left preconditioning
...
>>>>>>>>>>>>>
%%%%%%%%%%%%%%%%%%%%%%%%

So it seams that by using

PCMGGetSmoother ( pcMG, level , &subksp );

I was capable  to set both the pre- and post- smoothers to be PCASM
but everything I did after that applied only to the
pre-smoother, while the post-smoother got the default PCASM options.

I know that I can use
PCMGGetSmootherDown and PCMGGetSmootherUp, but that would 
probably double the memory allocation and the computational time in the ASM.

Is there any way I can just use PCMGGetSmoother 
and use the same PCASM in the pre- and post- smoother?

I hope I was clear enough.

Thanks a lot for your help,
Eugenio