[petsc-users] ASM vs GASM

[Mark Adams]

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> Allowing GASM to construct the "outer" subdomains from the non-overlapping
> "inner" subdomains, and using "exact" subdomain solvers (subdomain KSPs are
> using FGMRES+ILU with an rtol of 1e-12), I get convergence in ~2 iterations
> in the preconditioned residual norm to an rtol of 1e-12. If I look at the
> true residual norm, however, it stagnates around 1e-4.
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That PC is singular.
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