On Tue, Sep 20, 2011 at 11:45, Matija Kecman <matijakecman@gmail.com> wrote:

$ mpirun -np 1 ./ex3 -ksp_type gmres -pc_type none -m 100
Norm of error 0.570146 Iterations 0

This uses a nonzero initial guess so the initial residual norm is compared to the right hand side.

$ ./ex3 -ksp_type gmres -ksp_monitor -m 100 -pc_type none -ksp_converged_reason -info |grep Converged

[0] KSPDefaultConverged(): user has provided nonzero initial guess, computing 2-norm of preconditioned RHS

[0] KSPDefaultConverged(): Linear solver has converged. Residual norm 1.113646413065e-04 is less than relative tolerance 1.000000000000e-05 times initial right hand side norm 1.291007358616e+01 at iteration 0

You can use the true residual, it just costs something so it's not enabled by default:

$ ./ex3 -ksp_type gmres -ksp_monitor -m 100 -pc_type none -ksp_converged_reason -ksp_converged_use_initial_residual_norm

[many iterations]

Linear solve converged due to CONVERGED_RTOL iterations 1393

Norm of error 0.000664957 Iterations 1393