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## 8.1. Solver Parameters

Figure: Solver Parameters

• Solver: Algorithm to solve the iterative method. BICGSTAB (BiConjugate Gradient STAbilized method) and GMRES (Generalized Minimal Residual method) are available. If no convergence is achieved by using any of this methods, try to use the other one. The Max. number of unknowns for Direct Solver option is the threshold of the maximum allowed unknowns to compute the currents of the Method of Moments by using a direct solution method, instead of using the iterative process. For using always the iterative solver, set this parameter to zero. Note that the direct solution method may require huge memory and time resources when a large number of unknowns is considered.

• Preconditioner: The user can enable the preconditioner to speed up the resolution of the problem with the Enable Precondicioner option. The user can choose between two different preconditioners:
• Diagonal Preconditioner: The diagonal preconditioner is fast to compute and requires a reduced amount of memory, although the improvement in the convergence rate it produces is normally moderate. This preconditioner it is only recommended when more than 8 divisions per wavelenth is set in the meshing process, as a shorter number of divisions slows down the convergence instead not using this preconditioner.
• Sparse Approximate Inverse Preconditioner (SAI): This preconditioner will generally result in a faster convergence than the diagonal preconditioner. The Sparse Distance, expressed in wavelengths (0.25 as the default value) indicates how accurately this preconditioner will resemble the inverse of the rigorous MoM matrix. Higher values will normally involve a faster convergence, but the memory required to store the preconditioner data will grow fast, non-linearly. We advice to keep the default value or increase it slightly in case of specially ill-conditioned systems.

• Relative Error: It is the maximum value error allowed in the iterative process. When the relative error of any iteration is lower than the value specified, the current computation stay is considered as a valid solution and the iterative process is finished. The smaller is the Relative Error the more accurate is the provided solution, but the larger is the computation time.

• Maximum number iterations: Maximum number of iterative steps used to search an iteration that satisfies the specified Relative Error. If the maximum number of iterations is reached without getting a valid solution, the last iteration solution is saved.

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