[petsc-users] ASM vs GASM

Smith, Barry F. bsmith at mcs.anl.gov
Mon Apr 29 19:39:51 CDT 2019

  I believe so. Probably you've already done this but you can look at src/ksp/ksp/examples/tutorials ex62.c and ex64.c for sample usage.

  Do you get the same (correct) behavior for both when you use inner_ises but no outer (let GASM/ASM determine it)? What if you use the same outer as inner?

  Note that for ASM the "inner" subdomains can overlap while for GASM they cannot overlap (and of course their union needs to be all degrees of freedom).

  GASM is usually used where each inner is exactly several processes but it should work more generally as well.


> On Apr 29, 2019, at 7:10 PM, Griffith, Boyce Eugene via petsc-users <petsc-users at mcs.anl.gov> wrote:
> I am trying to setup a GASM preconditioner and am running into some difficulty getting convergence even with exact subdomain solvers. I am just doing things in serial now, and tried switching to ASM, and get convergence. I am wondering if I am misunderstanding the GASM interface. If inner_ises and outer_ises define the “inner” and “outer” subdomains for GASM, should GASM and ASM do the same things when configured via:
> 	PCGASMSetSubdomains(pc, n_subdomains, inner_ises, outer_ises);
> and
> 	PCASMSetLocalSubdomains(pc, n_subdomains, outer_ises, inner_ises);
> Thanks!
> — Boyce

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