[petsc-users] Termination criteria for solving linear system

Markus Bürg buerg at kit.edu
Tue Feb 2 06:30:25 CST 2010

Hello Thomas,

the precision of the solver does not correspond to the precision of the 
solution for your problem. If you do not want such a small residual in 
your problem, you have to reduce the number of degrees of freedom.

Best Regards,

Am 02.02.10 13:05, schrieb Thomas Witkowski:
> In my computations I use "bicg" preconditioned by "bjacobi" with an 
> absolute tolerance of 1^e-8 as termination criteria. After PETSc has 
> computed the solution, the code computes the residual. It is usually 
> in the magnitude of 1^-13. I'm not really sure what happens here. Is 
> it, because PETSc checks the preconditioned residual? If so, is there 
> a way to tune the termination criteria to the true residual? I would 
> like to save some computational time, since I do not need to solve the 
> system with this high precision.
> Regards,
> Thomas

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