[petsc-users] Trying to set up a field-split preconditioner

[subramanya sadasiva]

Hi Matt, I am using Libmesh so the DM stuff is actually in the background, and unfortunately the matrix doesn't have a saddle point, I thought that 

  -ch_solve_fieldsplit_block_size 2  -ch_solve_fieldsplit_0_fields 0  -ch_solve_fieldsplit_1_fields 1
would inform the solver of the structure. If this doesn't work owing to the fact that the problem is only being solved on a section of the mesh (because of the reduced space method), I guess I will have to use the PetscSection. Does that sound right?
Thanks, Subramanya   
Subject: Re: [petsc-users] Trying to set up a field-split preconditioner
From: knepley at gmail.com
To: potaman at outlook.com
CC: petsc-users at mcs.anl.gov; libmesh-users at lists.sourceforge.net

On Fri, Jul 19, 2013 at 7:56 PM, subramanya sadasiva <potaman at outlook.com> wrote:







Hi, 
I am trying to set up a fieldsplit preconditioner for my Cahn Hilliard solver and I get the following error, 
You have to tell the PCFIELDSPLIT about the dofs in each field. So

1) You are probably not using a DA, since it would tell it automatically
2) If you have a saddle point, you can use -pc_fieldsplit_detect_saddle_point

3) If none of those apply, you can set a PetscSection describing your layout to the DM for the solver.
     Since this is new, I suspect you will need help, so mail back.
  Thanks,

     Matt 
[0]PETSC ERROR: --------------------- Error Message ------------------------------------
[0]PETSC ERROR: Petsc has generated inconsistent data![0]PETSC ERROR: Unhandled case, must have at least two fields, not 0![0]PETSC ERROR: ------------------------------------------------------------------------

These are the options that I am using, -ch_solve is just a prefix. 


-ch_solve_pc_type fieldsplit
-ch_solve_pc_fieldsplit_type schur-ch_solve_fieldsplit_block_size 2-ch_solve_fieldsplit_0_field 1-ch_solve_fieldsplit_1_field 0-ch_solve_fieldsplit_0_ksp_type cg 
-ch_solve_fieldsplit_0_pc_type hypre-ch_solve_fieldsplit_0_pc_type_hypre boomeramg -ch_solve_fieldsplit_1_ksp_type cg-ch_solve_fieldsplit_1_pc_type hypre -ch_solve_fieldsplit_1_pc_type_hypre boomeramg

Any ideas?
Thanks,Subramanya 

 		 	   		  


-- 
What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.

-- Norbert Wiener
 		 	   		  
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