Hi, When I solve a linear system and monitor the true norm residual I got somethig like this (rtol is set to 1e-6) :
Residual norms for stokes_ solve. 0 KSP preconditioned resid norm 1.270103385648e+00 true resid norm 2.319288792500e+06 ||r(i)||/||b|| 1.667494921925e-01 1 KSP preconditioned resid norm 5.669390085343e-01 true resid norm 1.031308013796e+06 ||r(i)||/||b|| 7.414776812212e-02 2 KSP preconditioned resid norm 2.347505837595e-01 true resid norm 5.772588330636e+05 ||r(i)||/||b|| 4.150307524801e-02 3 KSP preconditioned resid norm 1.374434713779e-01 true resid norm 2.045693242518e+05 ||r(i)||/||b|| 1.470788417874e-02 4 KSP preconditioned resid norm 4.177447095627e-02 true resid norm 1.127811207483e+05 ||r(i)||/||b|| 8.108604100745e-03 5 KSP preconditioned resid norm 1.979676092561e-02 true resid norm 1.175236295643e+05 ||r(i)||/||b|| 8.449575410292e-03 6 KSP preconditioned resid norm 7.297213488366e-03 true resid norm 1.135209489825e+05 ||r(i)||/||b|| 8.161795399204e-03 7 KSP preconditioned resid norm 3.043016937820e-03 true resid norm 1.156795165002e+05 ||r(i)||/||b|| 8.316989542594e-03 8 KSP preconditioned resid norm 1.655126721698e-03 true resid norm 1.141320219921e+05 ||r(i)||/||b|| 8.205729606261e-03 9 KSP preconditioned resid norm 4.928188158108e-04 true resid norm 1.143795580962e+05 ||r(i)||/||b|| 8.223526665338e-03 10 KSP preconditioned resid norm 2.038487964289e-04 true resid norm 1.141943101596e+05 ||r(i)||/||b|| 8.210207927522e-03 11 KSP preconditioned resid norm 1.116161343513e-04 true resid norm 1.142236376429e+05 ||r(i)||/||b|| 8.212316480350e-03 Linear solve converged due to CONVERGED_RTOL iterations 11. I'd be thankful if I could get some clarification on a few things: - the unpreconditioned norm doesn't converge but if I visualize my solution it looks ok - the solver says that the solution has converged due to RTOL but it doesn't seem that r(11)/r(0) is less than 1e-6 I use GMRES with MG Preconditioning and GMRES+PCSHELL as smoother. The PCSHELL at each level also implies a pre-solve scaling of the solution and rhs vectors but these are also unscaled in a post-solve step. thanks, Domenico
