[Trilinos-Users] small question concerning ML

[Riccardo Rossi]

Dear list,

i am trying to use ILU0 smoother together with ML to see if it can improve
convergence, with a problem which corresponds to a pde size of 4


the thing is that if i use the following

            ML_Epetra::SetDefaults("NSSA", MLList, options, params);
            MLList.set("PDE equations", mNumDof);
             MLList.set("null space: add default vectors", true);
            MLList.set("aggregation: type","Uncoupled");

it works correctly

but if i put the following settings

       MLList.set("PDE equations", mNumDof);
       MLList.set("null space: add default vectors", true);
       MLList.set("aggregation: type","Uncoupled");  <----- up to this
point exactly identical

        MLList.set("smoother: type","IFPACK");
        MLList.set("smoother: ifpack type", "ILU");
        MLList.set("smoother: ifpack overlap", 0);
         MLList.sublist("smoother: ifpack list").set("fact: level-of-fill",
0);

         MLList.set("ML output",5);
        MLList.set("print unused",1);


than it does not even try to iterate and gives the output posted at the end
of the email (provding at the end a wrong result):

can anyone give a hint of what can i be doing wrong? changing overlap and
level of fill does not improve the situation
also commenting the line
     MLList.set("null space: add default vectors", true);
does not help

any suggestion is welcome

thank you in advance
Riccardo

System Solve Time : 5.44
Building Time : 2.86
ML_Aggregate_Coarsen (level 0) begins
ML_Aggregate_CoarsenUncoupled : current level = 0
ML_Aggregate_CoarsenUncoupled : current eps = 0.000000e+00
Aggregation(UVB) : Total nonzeros = 25542464 (Nrows=438016)
Aggregation(UVB) : Amalgamated matrix done
Aggregation(UC) : Phase 0 - no. of bdry pts  = 0
Aggregation(UC) : Phase 1 - nodes aggregated = 71810 (109504)
Aggregation(UC) : Phase 1 - total aggregates = 5698
Aggregation(UC_Phase2_3) : Phase 1 - nodes aggregated = 71027
Aggregation(UC_Phase2_3) : Phase 1 - total aggregates = 5698
Aggregation(UC_Phase2_3) : Phase 2a- additional aggregates = 237
Aggregation(UC_Phase2_3) : Phase 2 - total aggregates = 5935
Aggregation(UC_Phase2_3) : Phase 2 - boundary nodes   = 1226
Aggregation(UC_Phase2_3) : Phase 3 - leftovers = 0 and singletons = 0
ML_Aggregate_Coarsen (level 1) begins
ML_Aggregate_CoarsenUncoupled : current level = 1
ML_Aggregate_CoarsenUncoupled : current eps = 0.000000e+00
Aggregation(UVB) : Total nonzeros = 4840413 (Nrows=23740)
Aggregation(UVB) : Amalgamated matrix done
Aggregation(UC) : Phase 0 - no. of bdry pts  = 0
Aggregation(UC) : Phase 1 - nodes aggregated = 3526 (5935)
Aggregation(UC) : Phase 1 - total aggregates = 97
Aggregation(UC_Phase2_3) : Phase 1 - nodes aggregated = 3526
Aggregation(UC_Phase2_3) : Phase 1 - total aggregates = 97
Aggregation(UC_Phase2_3) : Phase 2a- additional aggregates = 25
Aggregation(UC_Phase2_3) : Phase 2 - total aggregates = 122
Aggregation(UC_Phase2_3) : Phase 2 - boundary nodes   = 2
Aggregation(UC_Phase2_3) : Phase 3 - leftovers = 0 and singletons = 0
ML_Aggregate_Coarsen (level 2) begins
ML_Aggregate_CoarsenUncoupled : current level = 2
ML_Aggregate_CoarsenUncoupled : current eps = 0.000000e+00
Aggregation(UVB) : Total nonzeros = 97790 (Nrows=488)
Aggregation(UVB) : Amalgamated matrix done
Aggregation(UC) : Phase 0 - no. of bdry pts  = 0
Aggregation(UC) : Phase 1 - nodes aggregated = 94 (122)
Aggregation(UC) : Phase 1 - total aggregates = 5
Aggregation(UC_Phase2_3) : Phase 1 - nodes aggregated = 94
Aggregation(UC_Phase2_3) : Phase 1 - total aggregates = 5
Aggregation(UC_Phase2_3) : Phase 2a- additional aggregates = 1
Aggregation(UC_Phase2_3) : Phase 2 - total aggregates = 6
Aggregation(UC_Phase2_3) : Phase 2 - boundary nodes   = 0
Aggregation(UC_Phase2_3) : Phase 3 - leftovers = 0 and singletons = 0
Smoothed Aggregation : operator complexity = 1.193356e+00.
Amesos (level 3) : NumGlobalRows = 24
Amesos (level 3) : NumGlobalNonzeros = 576
Amesos (level 3) : Fill-in = 100 %
Amesos (level 3) : Building KLU
Amesos (level 3) : Time for factorization  = 0.000393867 (s)

        *******************************************************
        ***** Problem: Epetra::CrsMatrix
        ***** Preconditioned GMRES (with condnum) solution
        ***** ML (L=4, ~/IFPACK_post0, ~/Amesos_KLU_3)
        ***** No scaling
        *******************************************************

                iter:    0           residual = 1.000000e+00


    ***************************************************************

    Warning: the GMRES Hessenberg matrix is ill-conditioned.  This may
    indicate that the application matrix is singular. In this case, GMRES
    may have a least-squares solution.

    Solver:            gmres_condnum
    number of iterations:    1

    Actual residual =  3.0313e+00    Recursive residual =  3.0313e+00

    Calculated Norms                Requested Norm
    --------------------------------------------    --------------

    ||r||_2 / ||r0||_2:        1.000000e+00    1.000000e-08

                -----------------------------------------------------

                Warning : The Hessenberg matrix is too small

                Analysis of the Hessenberg matrix:

                smallest eigenvalue (in module) = 1.000000e+00
                largest eigenvalue (in module)  = 1.000000e+00


    ***************************************************************

                estimated condition number      = 1.000000e+00

                -----------------------------------------------------


        Solution time: 0.594218 (sec.)
        total iterations: 1
Linear solver




-- 

Dr. Riccardo Rossi, Civil Engineer

Member of Kratos Team

International Center for Numerical Methods in Engineering - CIMNE
Campus Norte, Edificio C1

c/ Gran Capitán s/n

08034 Barcelona, España

Tel:        (+34) 93 401 56 96

Fax:       (+34) 93.401.6517
web:       www.cimne.com
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