Advanced

The node (

) is an attribute node that handles advanced settings for solver nodes, such as a Stationary Solver, Eigenvalue Solver, and Time-Dependent Solver. Also see About the Advanced Attribute Settings.

Use the list to control how the solver handles matrix symmetry of linear system matrices. Select:

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to override the automatic symmetry detection and force the solver to assume that matrices are nonsymmetric.

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to override the automatic symmetry detection and force the solver to assume that matrices are symmetric.

	Selecting Symmetric for a problem that does not result in symmetric matrices leads to an incorrect solution. See Which Problems are Symmetric? for information.

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to override the automatic symmetry detection and force the solver to assume that matrices are Hermitian.

The matrix format can be a sparse matrix or a full matrix, which you choose as or , respectively, from the list. The default format is ; this setting chooses a sparse or filled matrix format based on the solver used. In addition, you can choose a matrix-free format, which you choose as . This option assembles the matrix vector product when needed. This can reduce the memory usage significantly for solvers that support the following formats:

For other solvers, COMSOL Multiphysics automatically changes to another matrix format and issues a warning.

Even if variables are well scaled, equations can have very different scales. The check box is selected to balance the equations using row equilibration. Even when this check box is selected, row equilibration is not used in the following situations in order to preserve matrix symmetry:

Use the list to select a method for the computation of matrices needed for constraint handling (see Elimination Constraint Handling). Select:

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to let the software automatically determine the most appropriate method, which uses an explicit handling of nodal constraints and one of the Orthonormal or Sparse methods for the remaining constraints.

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to handle constraints by explicitly eliminating the DOFs on the destination side of the explicit constraints. The remaining constraints are handled using the Orthonormal method.

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to handle constraints by explicitly eliminating the DOFs on the destination side of the explicit constraints. The remaining constraints are handled using the Sparse method.

Explicit constraints are obtained when the Nodal constraint method is used for boundary conditions like Periodicity and Continuity on boundary pairs.

For the Automatic null-space function method, you can specify an , which is used in the automatic choice between Orthonormal and Sparse handling (for elemental constraints). If an estimate of the complexity (the number of operations) needed to SVD factorize the largest constraint block exceeds this limit, the Sparse method is used. Else the Orthonormal method is used. The limit is 107 per default. To SVD factorize a block with this complexity is usually fast, so you might want to increase this limit for increased constraint handling stability.

You can store the last residual while solving and also in the solver output, if you want to access it using the residual operator during postprocessing. Storing the residual in the output increases the memory requirements for the simulations. From the Store last residual list, choose

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, to make the last residual available while solving and also in the solver’s output so that you can access it during postprocessing.

The solver log contains information about the progress and convergence of the solvers (see The Log Window). From the list, choose one of the following formats:

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, which reports a minimal amount of information (for example, warnings and nonstandard feedback). The normal output (once per “step” and so forth) is turned off.

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(the default), which reports information about the main solver (the time-dependent solver, for example).

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, which reports information about the main solver and also information about the solver on the level below (a nonlinear stationary solver, for example).

For the time-dependent solvers, you can also specify an interval for the log sampling (in seconds) in the field. The default is 0.005 s, which means that the log is updated at most every 0.005 s. Increasing the sampling interval can reduce the overhead associated with the log when solving problems with many small time steps. Set the value to 0 to make the log contain every time step regardless of their size.

When the check box is selected, then under certain circumstances the scaling of the equations for the linear solvers can be changed to scales that are taken from the current solution. These circumstances are the following:

When this happens, COMSOL Multiphysics adds a printout of the new scales to the solver log.

This section contains some settings related to the assembly process when computing a solution.

By default, the solver chooses the number of mesh elements that are processed together during the assembly process (the block size). Select the check box for manual specification of a block size for all null-space function methods except Automatic.

Select the check box to control whether the solver treats such complex-valued output as an error or not.

The check box controls how the solver handles undefined mathematical operations such as division by zero.

Select the check box to make COMSOL Multiphysics check intermediate results for undefined numerical values (Inf or NaN) when numerical overflow occurs, for example. Selecting this option gives more accurate error messages when such undefined numerical values occur.

Select the check box to be able to override the solver mechanism that automatically detects which quantities need to be reassembled. This can be useful to improve efficiency in situations when the automatic mechanism is too sensitive and reassembles quantities that do not need to be reassembled.

If the check box is selected, the is by default.

The load (residual vector) is constant if the PDE and the Neumann boundary conditions are linear with time-independent coefficients and right-hand sides. For the discretized model, this means that the residual vector L depends linearly on U:

and that L0, K, D, and the mass matrix E are constant.

If you choose to turn the , it instructs the solver to perform a reassembly process for the computation of the residual vector (when ) or not. However, even if it is off, you might still want to treat some of the matrices as constant. Manual control of reassembly of these quantities can be controlled with the available check boxes, which makes the assembly only occur once for the corresponding matrix.

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Select the check box if you want to treat the coefficients of the first-order time-derivative terms or the second-order time-derivative terms as constant. In the discretized model, this means that the damping (sometimes called mass) matrix D or the mass matrix E is treated as constant.

If the check box is selected, you can control reassembly of the constraint residual. By default the is . The constraint is constant if the Dirichlet boundary conditions (constraints) are linear and time independent. For the discretized model, this means that the constraint residual M depends linearly on U (M = M0 − NU) and that M0 and N are constant. It is also assumed that the constraint Jacobian N is correct.

If you choose to turn the , it instructs the solver to perform a reassembly process for the computation of the constraint residual vector (when ) or not. However, even if it is off, the constraint Jacobian might still be constant. To control the reassembly of this quantity, select the check box if the Dirichlet boundary conditions are linear with time-independent coefficients (not right-hand side). For the discretized model this means that N is constant.