[petsc-users] difference between left and right pc

[Barry Smith]

  Is the "preconditioner" singular?  How about the matrix?  Is the "preconditioner" a linear operator? Did you try KSPFGMRES on it?


On Sep 19, 2012, at 10:01 AM, "Klaij, Christiaan" <C.Klaij at marin.nl> wrote:

> I'm solving a system with GMRES using the same preconditioner either on the left or on the right.
> For left preconditioning I get two orders of reduction for the preconditioned residual in 20 its:
> 
> 
> The solution is ok for left preconditioning but stuck to zero (the initial guess) for right preconditioning.

   Is it really ok? The true residual norm is much much worse in the left case after 20 iterations than the right case.  How are you judging the solution quality?

   Barry


> Shouldn't left and right preconditiong give similar results, what could be the reason for this behaviour?
> 
> 
> dr. ir. Christiaan Klaij
> CFD Researcher
> Research & Development
> E mailto:C.Klaij at marin.nl
> T +31 317 49 33 44
> 
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