[Trilinos-Users] aztecoo+sundance problem

[Gideon Simpson]

I should have posted this too:
AZ_check_input: Setup information on processor 0

         solver:                                 1
         convergence flag:                       0
         maximum iterations:                     5000
         reordering:                             1
         preconditioner:                         14
         polynomial order:                       3
         GMRES ill conditioning threshold:                       1.0e+11
         GMRES restart size:                     30
         orthogonalization:                      0
         tolerance:                              1.0e-12
         drop:                                   0.0e+00
         fill-in:                                        1
         overlap:                                        0
         typeoverlap:                            0

         Number of internal unknowns:            0
         Number of border  unknowns:             10691
         Total number of unknowns:               10691
         Number of external unknowns:            0
         Number of internal blocks:              0
         Number of border  blocks:               10691
         Total number of blocks:                 10691
         Number of external blocks:              0
         Number of processors:                   1
         Node number:                            0
         Number of neighbors:                    0
         Number of unknowns sent to neighbors:   0
======================================================================== 
=======

                 *******************************************************
                 ***** Problem: Epetra::CrsMatrix
                 ***** Preconditioned GMRES solution
                 ***** ILU(1) domain decomp. without overlap
                 ***** No scaling
                 ***** NOTE: convergence VARIES when the total number of
                 *****       processors is changed.
                 *******************************************************

                 iter:    0           residual = 1.000000e+00

*********************************************************************
*****  Condition number estimate for subdomain preconditioner on PE 0  
= 1.4400e+02
*********************************************************************

I'm getting this through sundance, not by explicit manipulation of  
the epetra matrices, so I hope this is the calculation you wanted.   
In addition, I did try adjusting the alpha and rho threshold  
parameters as described in the AztecOO User's Guide and saw no  
improvement.
-gideon

On Jan 17, 2007, at 10:04 PM, Mike Heroux wrote:

> Gideon,
>
> This is often a symptom of a poorly conditioned preconditioner.  In  
> other words, the LU factors of ILU are poorly conditioned, which  
> can be true even if your original matrix is well-conditioned.  You  
> can check if this is the case by calling the Condest() method on  
> your AztecOO object.  If the value comes back as 1E+14 or more,  
> then this is likely the issue.  It is possible to reduce the  
> condition number and still have an effective preconditioner by  
> using the absolute and relative threshold values to perturb the  
> diagonal of the preconditioner.  This is described in the AztecOO  
> User Guide, starting on page 27:
>
> http://software.sandia.gov/trilinos/packages/aztecoo/ 
> AztecOOUserGuide.pdf
>
> If this is not the problem, let us know.  Also, there may be other  
> simpler ways to reduce the condition number of the preconditioner,  
> but we need to know more about your problem and the particular ILU  
> parameters you are using.
>
> Mike
>
>
> From: trilinos-users-bounces at software.sandia.gov [mailto:trilinos- 
> users-bounces at software.sandia.gov] On Behalf Of Gideon Simpson
> Sent: Wednesday, January 17, 2007 7:52 PM
> To: trilinos-users at software.sandia.gov
> Subject: [Trilinos-Users] aztecoo+sundance problem
>
> I've been getting the following error when solving some problems  
> that come out of Sundance, using GMRES+DomainDecomposition+ILU
>
> ***************************************************************
>
> Warning: a breakdown in this method
> has occurred and solution has not converged.
>
> Solver: gmres
> number of iterations: 1
>
> Recursive residual = nan
>
> Calculated Norms Requested Norm
> -------------------------------------------- --------------
>
> ||r||_2 / ||r0||_2: 1.000000e+00 1.000000e-12
>
> ***************************************************************
>
>
>
> Solution time: 9.740000 (sec.)
> total iterations: 1
> Epetra ERROR -2, ../../../../packages/aztecoo/src/AztecOO.cpp, line  
> 824
> Solve failed! state = Crashed
> message=Aztec solver failed: numerical breakdown
> iters taken = 1
> final residual = nan
> matrix written to badMatrix.dat
> RHS vector written to badVector.dat
>
> The matrix and RHS data files look fine, and when I solve the  
> problem using an Amesos direct solver, the answer is consistent.  
> What is the nature of this error and how might I correct it?
>
> -Gideon Simpson
> Department of Applied Physics and Applied Mathematics
> Columbia University
>
>

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