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What's weak constraints and lm3 lm4?

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When I followed the manual to restructure the MOS transistor,I cannot understand the meaning of weak constraints and in Boundary Expressions Jn=-q*lm3 Jp=q*lm4.

3 Replies Last Post 18.06.2010, 15:27 GMT-4

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Posted: 1 decade ago 09.04.2010, 01:20 GMT-4
Two chapters in the "COMSOL Multiphysics Modeling Guide" might help:

-Search for "Interpreting Boundary Conditions":
The Lagrange multiplier adjusts to satisfy the requested Dirichlet condition.

The Lagrange mulitpliers are written as greek symbol µ or as lm...

-Also have a look at the chapter "The Weak Form".

Two chapters in the "COMSOL Multiphysics Modeling Guide" might help: -Search for "Interpreting Boundary Conditions": The Lagrange multiplier adjusts to satisfy the requested Dirichlet condition. The Lagrange mulitpliers are written as greek symbol µ or as lm... -Also have a look at the chapter "The Weak Form".

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Posted: 1 decade ago 18.06.2010, 14:57 GMT-4
I imported this example into COMSOL 4 and I'm also having trouble with the Lagrange multipliers. When I run the model, COMSOL can't compute the drain current Id because it is dependent on the lm3 and lm4 terms. How do I get around this?
I imported this example into COMSOL 4 and I'm also having trouble with the Lagrange multipliers. When I run the model, COMSOL can't compute the drain current Id because it is dependent on the lm3 and lm4 terms. How do I get around this?

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 18.06.2010, 15:27 GMT-4
Hi

if you imported a 3.5 example you should carefully check the equations, as I have noticed that not everything is correctly imported (i.e. name errors or index errors).
This gives you the occasion, too, to learn more on the COMSOL internals, such that next time you need some custom physics you'll write it out in one go

Have fun Comsoling
Ivar
Hi if you imported a 3.5 example you should carefully check the equations, as I have noticed that not everything is correctly imported (i.e. name errors or index errors). This gives you the occasion, too, to learn more on the COMSOL internals, such that next time you need some custom physics you'll write it out in one go Have fun Comsoling Ivar

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