[petsc-users] Petsc direct solver

[amrit poudel]

Thanks Satish for the clarification.

If I use the following run time option why does the mumps get ignored as per the warning shown down below?

-ksp_type preonly -pc_type none -pc_factor_mat_solver_package mumps

As I understand it, this should read, no Krylov subspace method, no preconditioner, use direct solver.

WARNING! There are options you set that were not used!
WARNING! could be spelling mistake, etc!
Option left: name:-pc_factor_mat_solver_package value: mumps



> Date: Fri, 9 Sep 2011 22:31:57 -0500
> From: balay at mcs.anl.gov
> To: petsc-users at mcs.anl.gov
> Subject: Re: [petsc-users] Fwd: nonzero prescribed boundary condition
> 
> On Fri, 9 Sep 2011, Hong Zhang wrote:
> 
> > amrit :
> > >
> > > If I run a program with the following runtime option (notice that I have not
> > > included -pc_type lu ), will the program use mumps to solve the linear
> > > system of equations directly, or does it  run with default gmres iterative
> > > solver? Why do we have to specify a preconditioner for a direct solver ?
> > >
> > >  -pc_factor_mat_solver_package mumps
> > 
> > You must include '-pc_type lu' to use mumps.
> > There are many preconditioners for solving linear system, lu is one of pcs,
> > and mumps is one of packages implement lu.
> 
> PETSc solver is organized as 2 parts: KSP, PC
> 
> With this organization - direct solvers are categorized under PC.
> Sure - you don't need gmres with a direct solver - so you would use:
> 
> --ksp_type preonly -pc_type lu
> 
> The reason this organization makes sense for us is - we easily support
> stuff like:
> 
> -ksp_type gmres -pc_type bjacobi -sub_pc lu [-sub_ksp preonly]
> 
> And as Hong mentioned - mumps is one of the direct solvers we provide
> interface to - other prominant one is superlu_dist. Both are
> accessiable with
> 
> '-pc_type lu -pc_factor_mat_solver_package [mumps or superlu_dist]' etc...
> 
> Satish
 		 	   		  
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