"Sun, Hui" <[email protected]> writes: > If I run ex34 using the command: > ./ex34 -pc_type none -ksp_type gmres -ksp_monitor_short > > I get the following output: > 0 KSP Residual norm 0.0289149 > 1 KSP Residual norm < 1.e-11 > Residual norm 9.14804e-15 > Error norm 0.00020064 > Error norm 5.18301e-05 > Error norm 4.90288e-08 > Time cost: 1.60657 4.67008 0.0784049 > > From the output, it seems that solving Poisson without a > preconditioner is actually faster than using multigrid as a > preconditioner. I think multigrid should do better than that.
Can't beat one iteration with on preconditioner. The right hand side (thus solution) is an eigenvector, so GMRES without preconditioning converges in one iteration always. The example could not be worse for testing solvers.
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