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Linear solvers

Last edited by Christophe Geuzaine

By default GetDP uses linear solvers from PETSc. (You can also compile GetDP with alternative linear solvers - see the GetDP documentation.) The choice of which particular linear solver to use for a given problem is handled directly through PETSc options, which can be specified:

  • on the command line (e.g. getdp test.pro -solve -ksp_type cg -pc_type ilu)
  • in the Resolution operations, with the SetGlobalSolverOptions[] function (e.g. SetGlobalSolverOptions["-ksp_type gmres -petsc_prealloc 400"];)
  • in a file :
    • either as default options in a .petscrc file in your home directory
    • or in an arbitrary file, specified to getdp with the -solver option (e.g. getdp test.pro -solve -solver "myoptions.txt")

Here are some useful PETSc options:

# To use GMRES+ILU(3) with a relative tolerance of 1e-12 and a restart of 300:
-ksp_rtol 1.e-12
-ksp_type gmres
-ksp_gmres_restart 300
-pc_type ilu
-pc_factor_levels 3
# To use PETSc's built-in direct LU solver
-ksp_type preonly
-pc_type lu
-pc_factor_mat_solver_package petsc
# To use the direct LU solver from UMFPACK
-ksp_type preonly
-pc_type lu
-pc_factor_mat_solver_package umfpack
# To use the direct LU solver from MUMPS
-ksp_type preonly
-pc_type lu
-pc_factor_mat_solver_package mumps
# To preallocate 300 nonzero elements per line in the matrix
-petsc_prealloc 300
# To see the residual
-ksp_monitor
# To use GMRES+Jacobi with a relative tolerance of 1e-12 and a restart of 100:
-ksp_rtol 1.e-12
-ksp_type gmres
-ksp_gmres_restart 100
-pc_type jacobi
-pc_factor_levels 3

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