[Trilinos-Users] AztecOO::Iterate error code -3: loss of precision

[Deparis Simone]

Other 2 possibilities for CG breakdown are
1- your preconditioner changes between iterates, for example in case you have inner iterations
2- your system (matrix or preconditioner) is not symmetric.

GMRES would cure 2), Flexible GMRES 1)
They are both available in Belos,

Best regards
Simone


> On 15 May 2015, at 21:49, Heroux, Mike <MHeroux at CSBSJU.EDU> wrote:
> 
> Denis,
> 
> This message is generated when the iterative method detects numerical
> breakdown.  Although it can in principle come from coding errors,
> especially if you have logic errors in formulating your linear system that
> might make the matrix or RHS values incorrect, it is more likely a symptom
> of a naturally poorly conditioned system.  This is almost certainly the
> case if you have other systems for which the solver works.
> 
> In these situations, you can experiment with different preconditioners
> that might be more robust.  Also, you could consider GMRES in this case,
> perhaps without restart.  It can be more robust in these situations.
> 
> Mike
> 
> 
> On 5/15/15, 1:55 PM, "Denis Davydov" <davydden at gmail.com> wrote:
> 
>> Dear all, 
>> 
>> I am getting this error when solving a poisson equation discretized with
>> hp-FEM and Lagrange basis functions.
>> The solver is CG. 
>> Any idea what could that be?
>> 
>> p.s. the error appears only for a very particular combination of h and p
>> refinement, 
>> perhaps it could be related to a particularly bad condition number of the
>> matrix?
>> 
>> Kind regards,
>> Denis 
>> 
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