Thank a lot for your info. I will give it a try. -Hung -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Barry Smith Sent: Tuesday, May 05, 2009 3:59 PM To: PETSc users list Subject: Re: Additive multilevel Schwarz preconditioner These preconditioners require a definition of the interpolation between levels, if that is available then additive multilevel Schwarz preconditioner is available and can be thought of as a variant of multigrid where the levels are visited additively instead of recursively (multiplicatively). The PCMG preconditioner is the tool in PETSc for handling multigrid/multilevel preconditioners. Once the PCMG is setup then you can choose the additive version with -pc_mg_type additive By default PETSc uses ILU as the smoother on each level. For a pure additive form of the algorithm you will want -mg_levels_pc_type jacobi You will also want to turn off the GMRES accelerator on each level by - mg_levels_ksp_type none Running with -ksp_view will show you exactly what options are being used. -help will give you the various other options. If you are lucky enough to be running on a structured grid and want piecewise linear or constant interpolation then you can use the PETSc DMMG solver to handle almost everything for you. See its manual page. Other wise you will need to set the interpolation operators yourself see the manual page for PCMGSetInterpolation() Barry Note: in my experience using a classical multigrid algorithm will always beat the use of the additive Schwarz multilevel algorithm because newer information is used as the calculation proceeds. The multilevel additive Schwarz method was an important step in understanding Schwarz and multilevel/multigrid algorithms but is not a particularly useful algorithm in practice. On May 5, 2009, at 1:52 PM, Nguyen, Hung V ERDC-ITL-MS wrote:

Hello,

Does PETSc supports additive multilevel Schwarz preconditioner? If yes, how to set/run it?

Thanks,

-hung