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Thanks Satish for the clarification.<br><br>If I use the following run time option why does the mumps get ignored as per the warning shown down below?<br><br>-ksp_type preonly -pc_type none -pc_factor_mat_solver_package mumps<br><br>As I understand it, this should read, no Krylov subspace method, no preconditioner, use direct solver.<br><br>WARNING! There are options you set that were not used!<br>WARNING! could be spelling mistake, etc!<br>Option left: name:-pc_factor_mat_solver_package value: mumps<br><br><br><br><div>> Date: Fri, 9 Sep 2011 22:31:57 -0500<br>> From: balay@mcs.anl.gov<br>> To: petsc-users@mcs.anl.gov<br>> Subject: Re: [petsc-users] Fwd: nonzero prescribed boundary condition<br>> <br>> On Fri, 9 Sep 2011, Hong Zhang wrote:<br>> <br>> > amrit :<br>> > ><br>> > > If I run a program with the following runtime option (notice that I have not<br>> > > included -pc_type lu ), will the program use mumps to solve the linear<br>> > > system of equations directly, or does it run with default gmres iterative<br>> > > solver? Why do we have to specify a preconditioner for a direct solver ?<br>> > ><br>> > > -pc_factor_mat_solver_package mumps<br>> > <br>> > You must include '-pc_type lu' to use mumps.<br>> > There are many preconditioners for solving linear system, lu is one of pcs,<br>> > and mumps is one of packages implement lu.<br>> <br>> PETSc solver is organized as 2 parts: KSP, PC<br>> <br>> With this organization - direct solvers are categorized under PC.<br>> Sure - you don't need gmres with a direct solver - so you would use:<br>> <br>> --ksp_type preonly -pc_type lu<br>> <br>> The reason this organization makes sense for us is - we easily support<br>> stuff like:<br>> <br>> -ksp_type gmres -pc_type bjacobi -sub_pc lu [-sub_ksp preonly]<br>> <br>> And as Hong mentioned - mumps is one of the direct solvers we provide<br>> interface to - other prominant one is superlu_dist. Both are<br>> accessiable with<br>> <br>> '-pc_type lu -pc_factor_mat_solver_package [mumps or superlu_dist]' etc...<br>> <br>> Satish<br></div> </div></body>
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