nonsymmetric dynamics

aggregation: aux: threshold [double]. The matrix entry A i,j is ignored if
L i,j < threshold ∗ max j,i≠j L i,j . Note: the diagonal
of A is also modified so that constants are
still in the null space (assuming that this was
true for the unmodified A). Default: 0.0.
6.5 Default Parameter Settings for Common Problem Types
The MultiLevelPreconditioner class provides default values for five different preconditioner
types:
1. Classical smoothed aggregation for symmetric positive definite or nearly symmetric
positive definite systems.
2. Classical smoothed aggregation-based 2-level domain decomposition
3. 3-level algebraic domain decomposition
4. Eddy current formulation of Maxwell’s equations
5. Energy-based minimizing smoothed aggregation suitable for highly convective nonsymmetric
fluid flow problems.
Default values are listed in Table 6. In the table, SA refers to “classical” smoothed aggregation
(with small aggregates and relative large number of levels), DD and DD-ML to
domain decomposition methods (whose coarse matrix is defined using aggressive coarsening
and limited number of levels). Maxwell refers to the solution of Maxwell’s equations.
NSSA is a nonsymmetric smoothed aggregation variant which may be appropriate for highly
nonsymmetric operators.
Default values for the parameter list can be set by ML Epetra::SetDefaults(). The
user can easily put the desired default values in a given parameter list as follows:
Teuchos::ParameterList MLList;
ML_Epetra::SetDefaults(ProblemType, MLList);
Teuchos::ParameterList MLList;
ML_Epetra::SetDefaults(ProblemType, MLList, options, params);
Teuchos::ParameterList MLList;
ML_Epetra::SetDefaults(ProblemType, MLList, options, params, true);
In the second usage, options and params are vectors that control the Aztec smoother. In
the third usage, the boolean argument true permits SetDefaults to override any previously
set parameters.
For DD and DD-ML, the default smoother is Aztec, with an incomplete factorization ILUT,
and minimal overlap. Memory for the two Aztec vectors, options and params, is allocated
using Teuchos reference-counted pointers, and so will be freed automatically.
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