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it was found unsymmetrical matrix
Posted Jul 17, 2016, 9:41 p.m. EDT Version 5.2 2 Replies
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hi：
my model was used by a heat transfer node ,when it compute to 4%,then it was found unsymmetrical matrix and it was no convergence.
Best Regards
wei wei
my model was used by a heat transfer node ,when it compute to 4%,then it was found unsymmetrical matrix and it was no convergence.
Best Regards
wei wei
2 Replies Last Post Jul 21, 2016, 11:21 a.m. EDT
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Posted:
8 years ago
Welcome to the "the solver gave up and all I've got to go on is this useless message" club. Someday COMSOL will have better error diagnostics, especially with regards to convergence and solver issues, once they realize that 99% of their existing users desperately need this to be productive. Unfortunately COMSOL seems hypnotized by App Builder. I guess there's a 1% that wants sugared up COMSOL apps. It'll be funny when those simplified, sugared up apps start putting up dialogs like "unsymmetrical matrix" and the lusers running them call for support.
Anyway, try a simpler, smaller structure and fool around with the mesh. That's what I do when the solver barfs.
Anyway, try a simpler, smaller structure and fool around with the mesh. That's what I do when the solver barfs.
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Posted:
8 years ago
Hi,
The fact that the stiffness matrix is unsymmetric is not directly related to the fact that you get non-convergence. This is just an informational message.
Symmetric matrices appear in many problems, typically when the physical problem is conservative in the sense that a potential exists. For many other problems, the stiffness matrix is unsymmetric.
The solver reports changes in the symmetry properties for two reasons:
- The solution of the linear problem in each iteration will need significantly longer time and more memory when the matrix is unsymmetric.
- It can serve as an indication that some new effect comes into action in your physical problem, for example a transition from elastic to plastic state in a structural mechanics problem.
Why your problem did not converge can thus not be deduced from the fact that you got an 'Unsymmetric matrix' message, but it does indicate some significant change in your problem, physically or numerically.
Regards,
Henrik
The fact that the stiffness matrix is unsymmetric is not directly related to the fact that you get non-convergence. This is just an informational message.
Symmetric matrices appear in many problems, typically when the physical problem is conservative in the sense that a potential exists. For many other problems, the stiffness matrix is unsymmetric.
The solver reports changes in the symmetry properties for two reasons:
- The solution of the linear problem in each iteration will need significantly longer time and more memory when the matrix is unsymmetric.
- It can serve as an indication that some new effect comes into action in your physical problem, for example a transition from elastic to plastic state in a structural mechanics problem.
Why your problem did not converge can thus not be deduced from the fact that you got an 'Unsymmetric matrix' message, but it does indicate some significant change in your problem, physically or numerically.
Regards,
Henrik