[petsc-users] MINRES accuracy for a SPD matrix

[Smith, Barry F.]

  You could run with -ksp_view_mat binary:afilename -ksp_view_rhs binary:afilename and email the file afilename to petsc-maint at mcs.anl.gov 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 <petsc-users at mcs.anl.gov> 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