[Trilinos-Users] ilut setting

[Hoang Giang Bui]

Hi Chris

I didn't see the range of value of ilut level of fill in Ifpack user 
guide yet. But looking in the code of Ifpack_ILUT, I'm quite sure that 
the level of fill indicates the number of nonzeros in the preconditioner 
compare to initial nonzeros. Therefore its value can be bigger than 1.

Giang Bui


On 09/18/2013 04:43 AM, Chris Jackson wrote:
>
> I don’t know if this applies to the one you are talking about, but I 
> recall that with one of the ILUT preconditioners the fill value is 
> expected to be between 0.0 and 1.0.  1.0 meant essentially we were 
> finding the inverse of the matrix.  Before we figured that out we were 
> always astounded that BiCGStab was converging in 2 iterations…
>
> Chris Jackson
>
> *From:*trilinos-users-bounces at software.sandia.gov 
> [mailto:trilinos-users-bounces at software.sandia.gov] *On Behalf Of 
> *Hoang Giang Bui
> *Sent:* Tuesday, September 17, 2013 6:28 PM
> *To:* Erik Boman
> *Cc:* trilinos-users at software.sandia.gov
> *Subject:* Re: [Trilinos-Users] ilut setting
>
> Hi Erik
>
> I tried to increase "fact: ilut level-of-fill" to 50.0 and it still 
> doesn't converge. In fact, with this value the preconditioner take 
> very long to compute. Is there other option we can set for Ifpack ILUT?
>
> Giang Bui
>
> On Tue, Sep 17, 2013 at 8:01 PM, Erik Boman <egboman at sandia.gov 
> <mailto:egboman at sandia.gov>> wrote:
>
> Giang Bui,
>
> You will not get exactly the same answer because the ILUT 
> implementations are different in AztecOO and Ifpack. Also, the meaning 
> of "fill" may be slightly different. Try increase the value of  "fact: 
> ilut level-of-fill" in the Ifpack parameter to see if you can make it 
> converge.
>
> Erik
>
> Hoang Giang Bui wrote:
>
> Dear Trilinos developers,
>
> Is there difference between 2 settings:
>
> solver_parameters.set("AZ_solver", "AZ_bicgstab")
> solver_parameters.set("AZ_kspace", 1000)
> solver_parameters.set("AZ_output", 100)
> solver_parameters.set("AZ_precond", "AZ_dom_decomp")
> solver_parameters.set("AZ_subdomain_solve", "AZ_ilut")
> solver_parameters.set("AZ_drop", 0.0)
> solver_parameters.set("AZ_ilut_fill", 10.0)
> aztec_solver.SetParameters(solver_parameter, true);
>
> And:
> solver_parameters.set("AZ_solver", "AZ_bicgstab")
> solver_parameters.set("AZ_kspace", 1000)
> solver_parameters.set("AZ_output", 100)
> solver_parameters.set("AZ_precond", "AZ_none")
> aztec_solver.SetParameters(solver_parameter, true);
> IFPreconditionerType = "ILUT"
> preconditioner_parameters.set("fact: ilut level-of-fill", 10.0);
> preconditioner_parameters.set("fact: drop tolerance", 0.0);
> overlap_level = 1
> mPrec = Teuchos::rcp(Factory.Create(IFPreconditionerType, &rA, 
> overlap_level));
> mPrec->SetParameters(preconditioner_parameters);
> aztec_solver.SetPrecOperator(&*(mpPrec->GetOperator()))
>
> I thought it all resulted in Additive-Schwartz preconditioner with 
> ILUT as local subdomain preconditioner. But it gives different 
> performance. The first setting works well but the second failed to 
> converge.
>
> Best regards
> Giang Bui
>
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>
>
>
> -- 
> With Best Regards !
> Giang Bui
>
> To learn and to excel
>

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