Linear solvers: Advanced options

Precision for the Conjugate Gradient

Maximum number of iterations for the Conjugate

Gradient

Maximum number of iterations to compute before stopping the iterative process. Two options are available to set the number of iterations:

• A linear function which takes two integers as inputs (A and B) defined as:

  $$ $N=A \times \left(number of degrees of freedom\right)+B$

• A fixed value N

Default value: Linear function with A = 1 and B = 1, which is the number of equations of the problem.

Precision of the preconditioner.

Flag indicating to verbosity level of the iterative process. Set to “Yes” to prompt the evolution of the iteration process during the solving.

Relative precision to satisfy before stopping the iterative process.

Default value: 1.0e-6

Maximum number of iterations for the GMRes

Maximum number of iterations to compute before stopping the iterative process. Two options are available to set the number of iterations:

• A linear function which takes two integers as inputs (A and B) defined as:

  $$ $N=A \times \left(number of degrees of freedom\right)+B$

• A fixed value N

Default value: Linear function with A = 1 and B = 1, which is the number of equations of the problem.

Precision of the preconditioner.

Default value: 1.0e-6

Filling factor of the ILUT preconditioner.

Default value: 6.0

Number of vectors to store in order to build Krylov space.

Default value: 120

Flag indicating to verbosity level of the iterative process. Set to “Yes” to prompt the evolution of the iteration process during the solving.

Default value: “No”

Specifies how to permute the columns of the matrix for sparsity preservation. The reordering methods are:

• Minimum degree on A^T + A, minimum degree ordering on the structure of A^T + A
• Minimum degree on A^T * A, minimum degree ordering on the structure of A^T * A;
• COLAMD, approximates minimum degree column ordering;
• Dissection (2D) [Automatic in 2D], use METIS for the reordering;
• Dissection (3D) [Automatic in 3D], use METIS for the reordering;

Default value: “Automatically specified reordering method”

Set the row pivoting method. Two choices are available:

• 0.0 to disable the pivoting;
• ]0.0, 1.0[ to use the relaxed partial pivoting;
• 1.0 to use the classical pivoting method.

Default value: 0.0

Specifies whether to perform iterative refinement, and in what precision to compute the residual.

Default value: “Without”

Specifies whether to use the symmetric mode. Symmetric mode gives preference to diagonal pivots and uses an (A^T + A)-based column permutation algorithm.

Default value: “Without”

Specifies whether to compute the reciprocal pivot growth.

Default value: “Without”

Specifies whether to compute the reciprocal condition number.

Default value: “Without”

Set the level of verbosity during the solving process. Four levels are available to decide what information will be prompted:

• 1- Only errors messages
• 2- Errors, warnings and main statistics
• 3- Errors, warnings and terse diagnostics
• 4- Errors, warnings and information on input and output parameters

Default value: “1- Only errors messages”

Set the options regarding disk usage. Four options are available:

• No, do not use the disk memory
• Automatic – Switch over to Out-of-core depending on the matrix size
• Yes – Default temporary directory
• Yes – Choice of the temporary directory

Default value: “No”

Set the reordering method to use. Five methods can be used:

• METIS
• AMD – Approximate Minimum Degree
• QAMD – AMD with quasi-dense rows detection
• PORD
• AMF

Default value: “Automatic – Choice in Mumps”

Set the memory limitation. It allows the user to limit the memory Mumps can use (in MB).

Default value: Unlimited

Only for MUMPS (Distributed). Set to define MPI Options. To enable MPI computations, the MPI number can be specified with the Thread number.

Default value: “No"