Struggling to understand error thresholds for COMSOL iterative solvers

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Hi, I have a question and I am wondering if anyone can help?

I am fairly new to COMSOL, although I have a fair bit of prior experience with CFD/numerical methods. I am trying to run a stationary EM wave, frequency domain simulation of microwaves heating some dielectric material. However, I am struggling to understand how the error threshold settings work for the iterative linear solvers.

I am using COMSOL v5.5. For the stationary linear solver, I am using GMRES with a geometric multigrid preconditioner. For the pre- and post-smoothers, I am using SOR Vector and for the coarse solver, I am solving direct (using Pardiso).

In the 'Stationary Solver' node, I have 'Relative tolerance' set to 0.001. In the 'Iterative' sub-node, I have 'Residual tolerance' set to 0.1 and 'Factor in error estimate' set to 2. However, when I solve, the error convergence (according to the convergence plot) is getting down to around 3e-7 (and flatlining around there), but the solver won't terminate. This seems to be significantly lower than the requested error thresholds.

Can someone please help me to understand how the specified residual thresholds translate into an error threshold that will cause the solver to terminate? It seems quite confusing.


0 Replies Last Post 6 mars 2025, 10:55 UTC−5
COMSOL Moderator

Hello Lee Strobel

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