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Fixed number of iterations (the default) to perform a fixed number of iterations each time the Coarse Solver is used.
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Use tolerance to terminate the Coarse Solver when a tolerance is fulfilled.
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Iterations or tolerance to terminate when the estimated tolerance is smaller than a specified tolerance or after a specified number of iterations, whichever comes first.
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Number of iterations (available when Termination technique is set to Fixed number of iterations or Iterations or tolerance). Use this field to specify the fixed number of iterations to perform (default: 10).
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Relative tolerance (available when Termination technique is set to Use tolerance or Iterations or tolerance). Use this field to specify the termination tolerance (default: 0.1).
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Maximum number of iterations (only available when Termination technique is set to Use tolerance). Use this field to enter a maximum number of iterations that the solver is allowed to take (default: 500). When this number of iterations has been performed without reaching the tolerance specified in the Relative tolerance field, the solver automatically stops with an error message.
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Direct, stored factorization (the default) to store the factorization. If two SCGS smoothers are used as presmoother and postsmoother of a Multigrid solver, with similar enough settings, they share the same stored factorization, which means that they only use half the memory.
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Direct to use a direct solver. The direct solver is slower than the default option to store the factorization, but it uses less memory.
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Iterative, GMRES to use the iterative method GMRES. When Iterative, GMRES has been selected from the Block solver list, the following options become available:
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Use the Tolerance field to specify the termination tolerance of GMRES (default: 0.02).
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Use the Number of iterations before restart field to specify how many iterations the solver should take between each restart (default: 100).
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If you use the SCGS algorithm as preconditioner, or as a smoother to a multigrid preconditioner when either of GMRES, Conjugate gradients, BiCGStab, or TFQMR is used as the linear system solver, use the Direct, stored factorization or the Direct option in the Block solver list in order to get a stationary preconditioner.
The Iterative, GMRES option in the Block solver list can be useful if you use the FGMRES method as a linear system solver because it can handle preconditioners that are not stationary. The GMRES option can also be useful if you use the SCGS algorithm as a smoother to a multigrid solver because GMRES can in some cases be faster than the direct solver if set to a high tolerance, although this advantage is less pronounced with SCGS than Vanka due to the smaller block size used by SCGS.
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The Aggressive check box is selected by default. By clearing this check box you get a slightly more expensive smoother that is more robust. If you are experiencing convergence issues it may help to disable this option.
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The Filter individual elements check box is selected by default and controls if the filtering is applied to individual elements or if the lines are first created and the algorithm then filter lines that cover eliminated DOFs that have already been used.
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Select the Apply filter to AMG levels only check box to ensure that the filter is applied to AMG only.
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From the Apply filter to elements list, choose Prioritize unique start elements (the default) to control if the start element is filtered. You can also choose Prioritize unique lines to filter the entire line, which might be less efficient, or choose None to use the algorithm used prior to version 6.0.
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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.
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The Reuse mesh data check box is also selected by default to control if the mesh data should be kept and reused. Clear this check box to regenerate the mesh data when needed, which saves memory but is slower.
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