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why does "Undefined value found in the stiffness matrix" means?

Posted Jun 24, 2013, 2:59 a.m. EDT RF & Microwave Engineering, Wave Optics, Modeling Tools & Definitions, Parameters, Variables, & Functions 5 Replies

Changhee Lee
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I'm trying to simulate Photonic crystal. As far as I know, there is no need for me to know the stiffness of material in the crystal.
However, when I click "compute", comsol always screen error message on T.T

In the model attatched, I intend to make a photonic crystal, such as 230nm thickness and square lattice structure.
Therefore, I give my boundaries Periodic bondary conditon and Scattering Boundary condition.

Anyway What is the problem with my model?
5 Replies Last Post Feb 17, 2015, 1:55 p.m. EST
Aman Yadav
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Posted: 1 decade ago Jun 27, 2013, 7:40 a.m. EDT
Hello,

I am facing the same problem for a 2D photonic crystal. Please let me know if you could figure out the problem.

Regards,
Aman
Hello, I am facing the same problem for a 2D photonic crystal. Please let me know if you could figure out the problem. Regards, Aman
Magnus Ringh COMSOL Employee

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Posted: 1 decade ago Jun 27, 2013, 8:58 a.m. EDT
Hi,

The "stiffness matrix" is a general concept for partial differential equations when solved numerically using the finite element method. It got its name from solid mechanics, which was one of the original applications for FEA, but it's also used in other contexts for the matrix K in the general linear equation system K*u = f.

The problem in a model with this error is likely that an undefined value like 0/0 appears in some of the stiffness matrix components, and that you run an eigenfrequency study. Check your material properties or other equation coefficients so that they are well defined; perhaps some value is unintentionally defined as zero.

Best regards,
Magnus
Hi, The "stiffness matrix" is a general concept for partial differential equations when solved numerically using the finite element method. It got its name from solid mechanics, which was one of the original applications for FEA, but it's also used in other contexts for the matrix K in the general linear equation system K*u = f. The problem in a model with this error is likely that an undefined value like 0/0 appears in some of the stiffness matrix components, and that you run an eigenfrequency study. Check your material properties or other equation coefficients so that they are well defined; perhaps some value is unintentionally defined as zero. Best regards, Magnus
Minu Prabhachandran Nair
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Posted: 1 decade ago Jul 17, 2014, 12:05 a.m. EDT

I'm trying to simulate Photonic crystal. As far as I know, there is no need for me to know the stiffness of material in the crystal.
However, when I click "compute", comsol always screen error message on T.T

In the model attatched, I intend to make a photonic crystal, such as 230nm thickness and square lattice structure.
Therefore, I give my boundaries Periodic bondary conditon and Scattering Boundary condition.

Anyway What is the problem with my model?


Hi,
I am also trying to simulate a photonic crystal with 220nm thickness and i am getting the same error when using eigen frequency solver.Did u fix the problem? Can anyone suggest a solution. I cjecked all boundary conditions and material parameters.But still it shows the same error.

Thanks
Minu
[QUOTE] I'm trying to simulate Photonic crystal. As far as I know, there is no need for me to know the stiffness of material in the crystal. However, when I click "compute", comsol always screen error message on T.T In the model attatched, I intend to make a photonic crystal, such as 230nm thickness and square lattice structure. Therefore, I give my boundaries Periodic bondary conditon and Scattering Boundary condition. Anyway What is the problem with my model? [/QUOTE] Hi, I am also trying to simulate a photonic crystal with 220nm thickness and i am getting the same error when using eigen frequency solver.Did u fix the problem? Can anyone suggest a solution. I cjecked all boundary conditions and material parameters.But still it shows the same error. Thanks Minu
Albert276
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Posted: 10 years ago Jan 23, 2015, 5:31 a.m. EST
I also face the same problem. I changed the study from stationary to time dependent, and the problem is solved. Hope this can help you!
I also face the same problem. I changed the study from stationary to time dependent, and the problem is solved. Hope this can help you!
Hannes Pfeifer
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Posted: 10 years ago Feb 17, 2015, 1:55 p.m. EST
Hi all,

I don't know, whether this is applicable in your specific problem, but I had a similar problem (www.comsol.com/community/forums/4-4/thread/49931), which was solved by setting the transform point in the solver configuration to the guessed eigenvalue of my problem.
I hope it helps.

Cheers,
Hannes
Hi all, I don't know, whether this is applicable in your specific problem, but I had a similar problem (http://www.comsol.com/community/forums/4-4/thread/49931), which was solved by setting the transform point in the solver configuration to the guessed eigenvalue of my problem. I hope it helps. Cheers, Hannes

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