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

Denis Davydov davydden at gmail.com
Mon May 18 04:26:56 EDT 2015

Dear Simone and Mike, 

Thanks for your prompt reply. 
So far it seems it is related to poor-conditioned system as 
with direct solvers I can go further and results look reasonable. 
I also notice that the AMG preconditioner is more robust but not enough 
to go through the complete hp-refinement cycle.

Kind regards,

> On 15 May 2015, at 22:00, Deparis Simone <simone.deparis at gmail.com> wrote:
> 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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