回复： Re: About unpreconditioned residuals in Left Preconditioned GMRES

[jiaxun hou <jiaxun_hou@xxxxxxxxxxxx>]

Thank you, Dave. But there is still a question: how can I get the residual vector in each iteration? It seems difficult to get it without modifying the GMRES codes.

Best regards,
Jiaxun
Dave May <dave.mayhem23@xxxxxxxxx> 写道：

Hi,
    You can use the function

PetscErrorCode PETSCKSP_DLLEXPORT KSPSetConvergenceTest(KSP ksp,PetscErrorCode (*converge)(KSP,PetscInt,PetscReal,KSPConvergedReason*,void*),void *cctx)

to define your own convergence test.

Cheers,
    Dave.

2008/2/2 jiaxun hou <jiaxun_hou@xxxxxxxxxxxx>:

Hi everyone,

I want to use the Left Preconditioned GMRES to solve a linear system, and the stopping criterion  must  be  based on the  actual residuals (b-Ax). But the  GMRES codes of PETSc seems to use the preconditioned residuals (B^-1(b-Ax)) only. In addition,  when I set KSPSetNormType(ksp,KSP_NORM_UNPRECONDITIONED), I receive the error message: "Currently can use GMRES with only preconditioned residual (right preconditioning not coded)". So, is there any way to set stopping criterion based on the actual residuals?

Best regards,
Jiaxun

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