Stopping criteria

[Nguyen, Hung V ERDC-ITL-MS]

Thank you for the info which is very helpful.

-Hung 



-----Original Message-----
From: petsc-users-bounces at mcs.anl.gov
[mailto:petsc-users-bounces at mcs.anl.gov] On Behalf Of Barry Smith
Sent: Thursday, January 15, 2009 12:05 PM
To: PETSc users list
Cc: petsc-users at mcs.anl.gov
Subject: Re: Stopping criteria


    When something so basic goes wrong. CG kicks out because the matrix is
not symmetric positive definite, you need to step back and understand more
about the matrix before worrying about running in parallel fast.

    So, yes, you should run sequentially to "play around" with the matrix.
You can use a MatType of MATAIJ in MatSetType() to have it automatically be
SEQAIJ on one process and MPIAIJ on more than one. or MATBAIJ for BAIJ
format.

    You can then try direct solver, for example, trivially to begin to
understand the matrix. You can also use MatIsSymmetric() to determine if it
truly is symmetric or something went wrong in assembly. You can also try
-pc_type none and see what happens.

    Barry



On Jan 15, 2009, at 10:24 AM, Nguyen, Hung V ERDC-ITL-MS wrote:

> Hello Matt,
>
>> however I would first check your matrix using -pc_type lu -ksp_type 
>> preonly
> to make sure its not singular.
>
> I got the error message below while running with option above. Do I 
> have to build a matrix with type of seqaij/seqbaij to run with the 
> -pc_type lu option?
>
> Thanks,
>
> -Hung
>
>
>
>  np ..       138524
>  np ..       143882
> [0]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [0]PETSC ERROR: [15]PETSC ERROR: [12]PETSC ERROR: [8]PETSC ERROR:
> --------------------- Error Message
> ------------------------------------
> [4]PETSC ERROR: [6]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [13]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> --------------------- Error Message
> ------------------------------------
> [15]PETSC ERROR: [13]PETSC ERROR: No support for this operation for 
> this object type!
> [12]PETSC ERROR: [15]PETSC ERROR: No support for this operation for 
> this object type!
> No support for this operation for this object type!
> [12]PETSC ERROR: Matrix type mpiaij  symbolic LU!
> Matrix type mpiaij  symbolic LU!
> [13]PETSC ERROR: [15]PETSC ERROR: [12]PETSC ERROR: Matrix type mpiaij 
> symbolic LU!
> [13]PETSC ERROR:
> ----------------------------------------------------------------------
> --
>
>
>
> -----Original Message-----
> From: owner-petsc-users at mcs.anl.gov 
> [mailto:owner-petsc-users at mcs.anl.gov
> ] On
> Behalf Of Matthew Knepley
> Sent: Wednesday, January 14, 2009 2:05 PM
> To: petsc-users at mcs.anl.gov
> Subject: Re: Stopping criteria
>
> On Wed, Jan 14, 2009 at 1:54 PM, Nguyen, Hung V ERDC-ITL-MS 
> <Hung.V.Nguyen at usace.army.mil> wrote:
>
>
>
> 	Hello All,
> 	
> 	I tried to solve an ill-conditioned system using cg with Jacobi
> 	preconditioned. The KSP solver was stopping due to diverged reason 
> within a
> 	few iterations. Is there a way to keep KSP solver running until 
> max_it?
>
>
> There is no way to continue CG here because it gets a zero divisor, 
> and interprets this as an indefinite matrix. You can try GMRES, 
> however I would first check your matrix using -pc_type lu -ksp_type 
> preonly to make sure its not singular.
>
>  Matt
>
>
>
> 	Thanks,
> 	
> 	-hung
> 	
> 	hvnguyen:jade23% aprun -n 16 ./test_matrix_read -ksp_type cg -pc_type

> jacobi
> 	-ksp_rtol 1.0e-15 -ksp_max_it 50000 -ksp_monitor 
> -ksp_converged_reason
> 	 0 KSP Residual norm 1.379074550666e+04
> 	 1 KSP Residual norm 7.252034661743e+03
> 	 2 KSP Residual norm 7.302184771313e+03
> 	 3 KSP Residual norm 1.162244351275e+04
> 	 4 KSP Residual norm 7.912531765659e+03
> 	 5 KSP Residual norm 4.094706251487e+03
> 	 6 KSP Residual norm 5.486131070301e+03
> 	 7 KSP Residual norm 6.367904529202e+03
> 	 8 KSP Residual norm 6.312767173219e+03
> 	Linear solve did not converge due to DIVERGED_INDEFINITE_MAT 
> iterations 9
> 	Time in PETSc solver: 0.452695 seconds
> 	The number of iteration       = 9
> 	The solution residual error = 6.312767e+03
> 	
> 	
>
>
>
>
> --
> 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
>