For some tests I use richardson iterations with direct solver for preconditioning (if everything is fine, richardson should be replaces by preonly).
-ksp_type richardson -pc_type lu -pc_factor_mat_solver_package mumps -ksp_monitor -ksp_monitor_true_residual -ksp_max_it 10 For some matrices I see that it converges fine in true residual norm but not in the preconditioned one: 0 KSP Residual norm 1.540366130785e+05 0 KSP preconditioned resid norm 1.540366130785e+05 true resid norm 4.257656834616e+04 ||r(i)||/||b|| 1.000000000000e+00 1 KSP Residual norm 1.355077212761e+05 1 KSP preconditioned resid norm 1.355077212761e+05 true resid norm 1.468758291284e-11 ||r(i)||/||b|| 3.449686877867e-16 2 KSP Residual norm 3.775360693480e+05 2 KSP preconditioned resid norm 3.775360693480e+05 true resid norm 5.008860262312e-12 ||r(i)||/||b|| 1.176435879376e-16 3 KSP Residual norm 1.714431257209e+05 3 KSP preconditioned resid norm 1.714431257209e+05 true resid norm 5.365631839419e-12 ||r(i)||/||b|| 1.260231166541e-16 4 KSP Residual norm 7.164219897555e+04 4 KSP preconditioned resid norm 7.164219897555e+04 true resid norm 5.582291603774e-12 ||r(i)||/||b|| 1.311118256030e-16 5 KSP Residual norm 2.480147180914e+05 5 KSP preconditioned resid norm 2.480147180914e+05 true resid norm 5.464714292269e-12 ||r(i)||/||b|| 1.283502758569e-16 6 KSP Residual norm 1.749548383255e+05 6 KSP preconditioned resid norm 1.749548383255e+05 true resid norm 6.601924132117e-12 ||r(i)||/||b|| 1.550600339239e-16 7 KSP Residual norm 1.873773824295e+05 7 KSP preconditioned resid norm 1.873773824295e+05 true resid norm 6.368611865551e-12 ||r(i)||/||b|| 1.495802060366e-16 8 KSP Residual norm 2.610223461339e+05 8 KSP preconditioned resid norm 2.610223461339e+05 true resid norm 8.365362648969e-12 ||r(i)||/||b|| 1.964780858090e-16 9 KSP Residual norm 2.459609758347e+05 9 KSP preconditioned resid norm 2.459609758347e+05 true resid norm 8.427381039077e-12 ||r(i)||/||b|| 1.979347177668e-16 10 KSP Residual norm 1.611793769272e+05 10 KSP preconditioned resid norm 1.611793769272e+05 true resid norm 8.325158481093e-12 ||r(i)||/||b|| 1.955338066095e-16 Would could be the reason for? Thomas
