SOR
The SOR node () handles settings for the SOR (successive overrelaxation) iterative method. Right-click the Iterative, Krylov Preconditioner, Presmoother, Postsmoother, or Coarse Solver attribute nodes to add an SOR node.
See The SOR Method for more detailed information about this feature.
General
Settings When Used with Any Attribute Node
Use the Solver list to specify which variant of the SOR algorithm to use. Select:
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SSOR (the default) to use the symmetric SOR algorithm, which in each iteration performs one SOR sweep followed by one SORU sweep.
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SOR to use the forward SOR algorithm.
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SORU to use the backward SOR (SORU) algorithm.
Settings When Not Used with Coarse Solver
Enter the Number of iterations to perform when this node is used as a preconditioner or smoother. This setting is not considered when the attribute is used as a linear system solver (with the Use preconditioner option in the Solver list of the Iterative attribute node). The solver then iterates until the relative tolerance specified by the corresponding operation node is fulfilled rather than performing a fixed number of iterations.
Settings When Used With a Coarse Solver
If this node is used with a Coarse Solver, select a Termination technique to determine how to terminate the solver. Select Fixed number of iterations to perform a fixed number of iterations each time the Coarse Solver is used, or Use tolerance to terminate the Coarse Solver when a tolerance is fulfilled.
If Fixed number of iterations is selected, enter a value for the Number of iterations to perform. The default is 10.
If Use tolerance is selected, enter a value for each of the following:
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Relative tolerance to specify the termination tolerance. The default is 0.1.
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Maximum number of iterations that the solver is allowed to take. When this number of iterations has been performed without reaching the tolerance specified in the Relative tolerance field, the solver is automatically stopped with an error message.
General Settings
Specify a scalar Relaxation factor ω. The allowed values of this factor are between 0 and 2 (default: 1). See About the Relaxation Factor for more information.
The Blocked version check box is selected by default and it uses a blocked version of the SOR method that is optimized for parallel computations. M is then constructed from a column-permuted version of A.
Select the Reuse data check box (selected by default) to reuse the data in the blocks that define the SOR method. If you have selected that check box, the Reuse sparsity pattern check box is available. It is elected by default to store the sparsity patterns of the assembled matrices and try to reuse them for successive assembly processes within the same solution process. In many cases, the sparsity pattern of the system matrices does not change from one nonlinear iteration or time step to the others. Reusing the sparsity pattern from the previous iteration or step can then improve the solution performance at the cost of a usually small amount of memory.
Settings with and Without a Coarse Solver
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If used with a Coarse Solver, select a Termination technique. These are described for the SCGS attribute under Settings When Used With a Coarse Solver.
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If a Coarse Solver is not used, enter the Number of iterations to specify a fixed number of iterations to perform when this attribute is used as a preconditioner or smoother (default: 2).
This setting is not considered when the attribute is used as a linear system solver (with the Use preconditioner option in the Solver list of the Iterative node). The solver then iterates until it has established convergence or has reached the maximal number of iterations as specified by the corresponding Iterative node, rather than perform a fixed number of iterations.