SOR Line
The SOR Line node () handles settings for the SOR line iterative method. This is a method of SOR type with added functionality useful for, for example, anisotropic meshes. It is a block SOR solver, where the blocks are formed from lines of nodes that are relatively close to each other. In addition, ordinary SSOR iterations are performed for all degrees of freedom after the SOR Line iterations have been performed. This node can be used together with the Iterative, Krylov Preconditioner, Presmoother, Postsmoother, or Coarse Solver nodes. Also see The SOR Line Algorithm.
Main
Settings When Used With Any Attribute Node
From the Sweep type list, choose SSOR (the default), SOR, or SORU. This setting decides in which order the blocks are looped through. SOR means lexical order (or forward), the order they are stored, while SORU means the opposite (backward) order. SSOR means SOR followed by SORU. The sweep type also decides if SOR, SORU, or SSOR is used in the secondary iteration (called SSOR update when the algorithms are described).
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
Use the Relaxation factor field to specify a scalar relaxation factor that controls the damping of the block SOR smoothing steps. The allowed values of this factor are between 0 and 2 (default: 0.5). See About the Relaxation Factor for more information.
Use the Line based on list to control if the lines of nodes are based on the Mesh (the default) or on a Matrix. Also define the Maximum line length (default: 20). This values determines the maximum length of the lines in number of DOFs for each block.
Use the Multivariable method list to control the line updates:
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If Uncoupled is selected, each block SOR smoothing step updates a set of degrees of freedom with the same name that are located on a line.
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If Coupled is selected (the default), each block SOR smoothing step updates all degrees of freedom located on a line.
For smoothing of the turbulence variables K and ε, Coupled is recommended.
The Blocked version check box is selected by default and it uses a version of the SOR method that is optimized for parallel computations.
Select the Reuse data check box (selected by default) to reuse data in order to improve the efficiency of the SOR Line method. If you have selected that check box, these additional check boxes are available:
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The Reuse lines check box is selected by default to also reuse the SOR lines of nodes. Note that when lines are reused as a performance enhancement, it is not fully certain that the optimal lines are used.
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The Reuse sparsity pattern check box is selected 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).
Secondary
Use the Number of secondary iterations field to specify the number of SSOR iterations to perform after the SOR Line iterations have been performed (default: 1).
Use the Relaxation factor field to specify a scalar relaxation factor that controls the damping of the SSOR updates for the iterations specified in the Number of secondary iterations field. The allowed values of this factor are between 0 and 2 (default: 0.7). See About the Relaxation Factor for more information.