About unpreconditioned residuals in Left Preconditioned GMRES

jiaxun hou jiaxun_hou at yahoo.com.cn
Sat Feb 2 06:49:03 CST 2008

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,
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