You could run with -ksp_view_mat binary:afilename -ksp_view_rhs binary:afilename and email the file afilename to [email protected] with the options you've used for a particularly clear case and we can take a look at it. Conventional wisdom is for SPD matrices CG is slightly better than MINRES but that is only conventional wisdom.
Barry > On Jul 30, 2019, at 2:03 PM, Mohammad Gohardoust via petsc-users > <[email protected]> wrote: > > 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
