Out of memory during LU factorization

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Could you help to understand what is wrong in my model? I get not converged solution error. You can find the model in attachment



6 Replies Last Post 01.10.2024, 11:48 GMT-4
Robert Koslover Certified Consultant

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Posted: 1 week ago 27.09.2024, 12:55 GMT-4

Looks like you are simply running out of memory. There are many ways to address this. See https://www.comsol.com/support/knowledgebase/830 and https://www.comsol.com/support/knowledgebase/1030

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
Looks like you are simply running out of memory. There are many ways to address this. See https://www.comsol.com/support/knowledgebase/830 and https://www.comsol.com/support/knowledgebase/1030

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Posted: 4 days ago 30.09.2024, 10:29 GMT-4
Updated: 4 days ago 30.09.2024, 11:08 GMT-4

Hi, my mesh is composed by about 1400000 tetrahedral elements (i suppose they are linear tetrahedral, let me know if there is a way to check). I have 4 dependent variables (electric field components and 1 S-parameter), so the number of degrees of freedom should be 0.2*1400000*4= 1200000 more or less. So less than 5 Gb of Physical memory should be enough according to comsol documentation (https://www.comsol.it/blogs/much-memory-needed-solve-large-comsol-models). The Log of my simulation says this

Compile Equations: Frequency Domain in Study 1/Solution 1 (sol1) ---------
Started at Sep 30, 2024, 4:10:09 PM.
Geometry shape function: Quadratic Lagrange
Running on 4 x Intel(R) Xeon(R) Gold 6154 CPU at 3.00 GHz.
Using 4 sockets with 2 cores in total on rat4.rfx.local.
Available memory: 773.70 GB.
Canceled
Time: 9 s.
Physical memory: 6.36 GB
Virtual memory: 21.79 GB
Ended at Sep 30, 2024, 4:10:18 PM.
----- Compile Equations: Frequency Domain in Study 1/Solution 1 (sol1)

So it looks like it is using more than 6 GB and still is going out of memory. Why?

Hi, my mesh is composed by about 1400000 tetrahedral elements (i suppose they are linear tetrahedral, let me know if there is a way to check). I have 4 dependent variables (electric field components and 1 S-parameter), so the number of degrees of freedom should be 0.2\*1400000\*4= 1200000 more or less. So less than 5 Gb of Physical memory should be enough according to comsol documentation (https://www.comsol.it/blogs/much-memory-needed-solve-large-comsol-models). The Log of my simulation says this Compile Equations: Frequency Domain in Study 1/Solution 1 (sol1) --------- Started at Sep 30, 2024, 4:10:09 PM. Geometry shape function: Quadratic Lagrange Running on 4 x Intel(R) Xeon(R) Gold 6154 CPU at 3.00 GHz. Using 4 sockets with 2 cores in total on rat4.rfx.local. Available memory: 773.70 GB. Canceled Time: 9 s. Physical memory: 6.36 GB Virtual memory: 21.79 GB Ended at Sep 30, 2024, 4:10:18 PM. ----- Compile Equations: Frequency Domain in Study 1/Solution 1 (sol1) So it looks like it is using more than 6 GB and still is going out of memory. Why?

Henrik Sönnerlind COMSOL Employee

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Posted: 4 days ago 30.09.2024, 11:11 GMT-4

As you can see in the attached printout, you are using second-order elements. So the DOF count is much larger. The number of DOF is printed in the Messages tab when you start the analysis.

You select the order of the elements in the Discretization section in the settings for the physics interface.

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Henrik Sönnerlind
COMSOL
As you can see in the attached printout, you are using second-order elements. So the DOF count is much larger. The number of DOF is printed in the Messages tab when you start the analysis. You select the order of the elements in the Discretization section in the settings for the physics interface.

Edgar J. Kaiser Certified Consultant

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Posted: 4 days ago 30.09.2024, 11:31 GMT-4

With linear discretization it takes about 32 GB and it completes. The mesh may be finer than needed. You can save a lot of memory by adjusting the mesh.

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
With linear discretization it takes about 32 GB and it completes. The mesh may be finer than needed. You can save a lot of memory by adjusting the mesh.

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Posted: 3 days ago 01.10.2024, 10:33 GMT-4

Ok thank you for the help. I have another doubt, as you can see my model is perfectly symmetryc with respect to the zx plane, so I wonder If can simulate only half of my geometry to save computational resources and time. I already did this in other models, but the problem now is that on the symmetry plane my fields (the fields of a input TE10 mode) are both tangent to the plane, so I can't use PMC or PEC boundary conditions, rigth?. What boundary condition would you suggest me to use in this case?

Thank you in advance

Ok thank you for the help. I have another doubt, as you can see my model is perfectly symmetryc with respect to the zx plane, so I wonder If can simulate only half of my geometry to save computational resources and time. I already did this in other models, but the problem now is that on the symmetry plane my fields (the fields of a input TE10 mode) are both tangent to the plane, so I can't use PMC or PEC boundary conditions, rigth?. What boundary condition would you suggest me to use in this case? Thank you in advance

Edgar J. Kaiser Certified Consultant

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Posted: 3 days ago 01.10.2024, 11:48 GMT-4

The E-field is perpendicular to the symmetry plane, no?

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
The E-field is perpendicular to the symmetry plane, no?

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