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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Convergence problem

Posted 15.03.2012, 10:55 GMT-4 RF & Microwave Engineering Version 4.2a 3 Replies

Kyle Chen
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Is there any idea on how to improve the convergence problem?
As shown in the attached picture, I have several point to calculate, but I cannot get convergence at the last point. I have refined the mesh several times, but the results still the same. Is there any way to improve the convergence?

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3 Replies Last Post 19.03.2012, 18:34 GMT-4
Alexander Kuznetsov
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Posted: 1 decade ago 15.03.2012, 14:30 GMT-4
Try either changing iterative solver settings or switching to direct solver.
Try either changing iterative solver settings or switching to direct solver.
Kyle Chen
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Posted: 1 decade ago 19.03.2012, 16:41 GMT-4
hi,

I have looked at the information about the iterative solver settings and direct solver, but there is no criteria on how to change this setting. For example, which setting is suitable for which application. What is the difference between the direct solver and iterative solver. Why the default setting is iterative solver? The Help only tells the users can put some values in the blank, but I don't know what is the effect of this setting. It takes a lot of time to see what happen if I change some of them. Is there any document on tutoring the solver setting?
hi, I have looked at the information about the iterative solver settings and direct solver, but there is no criteria on how to change this setting. For example, which setting is suitable for which application. What is the difference between the direct solver and iterative solver. Why the default setting is iterative solver? The Help only tells the users can put some values in the blank, but I don't know what is the effect of this setting. It takes a lot of time to see what happen if I change some of them. Is there any document on tutoring the solver setting?
Alexander Kuznetsov
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Posted: 1 decade ago 19.03.2012, 18:34 GMT-4
Direct solver gives exact solution of the matrix equation. But it's slower. Iterative solver gives approximate solution by going in subsequent iteration steps. Generally faster but might have problems with convergence.
Good starting point would be a book on FEM or numerical methods in linear algebra.
Direct solver gives exact solution of the matrix equation. But it's slower. Iterative solver gives approximate solution by going in subsequent iteration steps. Generally faster but might have problems with convergence. Good starting point would be a book on FEM or numerical methods in linear algebra.

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