Follow up CG and PC question

[KClimp at psl.nmsu.edu]

PETSC Help,

 

This e-mail is a follow up to the one Matt Funk wrote last week.  I work
with matt at NMSU and just wanted to give a little more information to
try and solve our problem.

 

The issue in a nutshell is we are solving our linear system using PETSC
to experiment with different solvers and PCs.  We have had great success
with GMRES and BICG using Jacobi and block Jacobi and CG with no PC.
The problem is when we try to run CG w/ the jacobi or bjacobi.

 

Shown below are some results when our system was ran with CG and no pc
and CG and Jacobi.

 

Shown below is the ksp_view information for the system using no PC.  It
converges at 302 iterations and the solution vector is very accurate
relative to our other results.

 

CASE 1: CG AND NO PC

========================================================================
========

Time Step #1 and Total Time 0.001 msec

call lrmodel()

call asm2_rhs()

KSP Object:

  type: cg

  maximum iterations=10000

  tolerances:  relative=1e-05, absolute=1e-50, divergence=10000

  left preconditioning

PC Object:

  type: none

  linear system matrix = precond matrix:

  Matrix Object:

    type=aij, rows=8192, cols=8192

    total: nonzeros=48640, allocated nonzeros=156280

      not using I-node routines

Norm of error 1.59444e-07, Iterations 302

 

 

CASE 2: CG AND JACOBI PC

Shown below is the same system as above with the only change being
-pc_type cg added at runtime.  The ksp_view and ksp_monitor information
are shown here.  KSP reports a residual norm of 1.27 then does not
iterate any more.  This is what matt described as does not run. 

========================================================================
========

Time Step #1 and Total Time 0.001 msec

call lrmodel()

call asm2_rhs()

  0 KSP Residual norm 1.270723190170e+00

KSP Object:

  type: cg

  maximum iterations=10000

  tolerances:  relative=1e-05, absolute=1e-50, divergence=10000

  left preconditioning

PC Object:

  type: jacobi

  linear system matrix = precond matrix:

  Matrix Object:

    type=aij, rows=8192, cols=8192

    total: nonzeros=48640, allocated nonzeros=156280

      not using I-node routines

Norm of error 0.0160078, Iterations 1

 

 

I hope that this will help diagnosis the problem and the issue is a
simple mistake on our part.  

 

Thank you guys for helping beginner users like me.

 

 

Kevin Climp

Target and Missile Systems 

Physical Science Laboratory-New Mexico State University

Phone - (505) 646-9244

 

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