Are you saying that the MINRES error is larger than CG error? In which norm? And which norm are you using for CG? (Output from -ksp_monitor_true_residual -ksp_view would be useful.)
CG does find a solution that is optimal in a different inner product, though this is usually pretty benign unless you have a poor preconditioner. Mohammad Gohardoust via petsc-users <[email protected]> writes: > Hi, > > I am trying to evaluate different solver/preconditioner combinations for > solving Richards' equation in porous media. The coefficient matrix is > symmetric positive definite and is usually solved by CG solver. I tried > MINRES with various preconditioners. The solution is acceptable but with > somehow considerable errors (compared to other solvers) which requires me > to decrease the tolerance threshold in my Picard iteration leading to > larger computation time. I would like to know if this is common for MINRES > and how to possibly overcome this? > > Thanks, > Mohammad
