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mass matrix is zero

Posted 6 mai 2010, 14:08 UTC−4 1 Reply

Susant Patra
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Hi,

While solving 1D Helmholtz equation with eigenvalue solver, I am receiving "mass matrix is zero" error. How can I correct it? In my equation setup coefficients "c" and "a" are non-zero and rest are zero.

Thanks for your help.

Regards,
Susant
1 Reply Last Post 19 juin 2012, 17:53 UTC−4
COMSOL Moderator

Hello Susant Patra

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Kevin McIlhany
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Posted: 1 decade ago 19 juin 2012, 17:53 UTC−4
The short answer is not to use the "Helmholtz Eqn" option when setting up a model. It makes too many assumptions about how you want to reach a solution and it imposes the need to define a mass matrix despite the fact that an eigenvalue problem may or may not have a mass matrix.

The easy fix it to start the model in "PDE Coefficient" mode and simply set the parameters up to be the same as the Helmholtz Eqn. This will work and it won't complain about a "mass matrix".

Good Luck.

-Kevin
The short answer is not to use the "Helmholtz Eqn" option when setting up a model. It makes too many assumptions about how you want to reach a solution and it imposes the need to define a mass matrix despite the fact that an eigenvalue problem may or may not have a mass matrix. The easy fix it to start the model in "PDE Coefficient" mode and simply set the parameters up to be the same as the Helmholtz Eqn. This will work and it won't complain about a "mass matrix". Good Luck. -Kevin

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