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About Integration in Comsol

Posted Jun 28, 2010, 9:12 a.m. EDT 3 Replies

chen wei
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Hi, guys!

I met a problem on Integration when I use Comsol to calculate Lennard-Jones Potential. I wanna know: in 3D, how to deal with "int_v1(dV1)int_v2(f(r)dV2)", dV1=dx1dy1dz1,dV2= dx2dy2dz2, v1 is subdomain1, v2 is subdomain2 and f(r) is the function of distance of dV1 and dV2, as shown EQ2 in attachment. Should I use PDE fomulation or integration coupling variables?

Thanks a lot!!!!!
Best Regards

Come on buddies!

Attachments:

3 Replies Last Post Jun 30, 2010, 4:24 p.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jun 28, 2010, 10:37 a.m. EDT
Hi

have you checked how to use the "dest()" operator on the different source and destination domains ?

I believe this is jut writing out plainvise your integration equation, no ?

Have fun Comsoling
Ivar
Hi have you checked how to use the "dest()" operator on the different source and destination domains ? I believe this is jut writing out plainvise your integration equation, no ? Have fun Comsoling Ivar
chen wei
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Posted: 1 decade ago Jun 30, 2010, 12:38 p.m. EDT

Hi

have you checked how to use the "dest()" operator on the different source and destination domains ?

I believe this is jut writing out plainvise your integration equation, no ?

Have fun Comsoling
Ivar


Thank you! "dest" seems to be great!

But, one more question, when I use "integration coupling variable" in postprocessing, it appears only one CPU do work, actually I have 8 CPUs and use "-np 8 -64 ", however solving will, as expected, use all 8 CPUs. Is postprocessing can only use one CPU? Is there any way to work around it?

How about use PDE or ODE to tackle my problem?
[QUOTE] Hi have you checked how to use the "dest()" operator on the different source and destination domains ? I believe this is jut writing out plainvise your integration equation, no ? Have fun Comsoling Ivar [/QUOTE] Thank you! "dest" seems to be great! But, one more question, when I use "integration coupling variable" in postprocessing, it appears only one CPU do work, actually I have 8 CPUs and use "-np 8 -64 ", however solving will, as expected, use all 8 CPUs. Is postprocessing can only use one CPU? Is there any way to work around it? How about use PDE or ODE to tackle my problem?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jun 30, 2010, 4:24 p.m. EDT
Hi

well COMSOL set up the problems to multiple CPU when it can, but it cannot always, if you look carfully at a solving sequence (typially a non-linear one) you will notice that often you switch between 1 and N cpus, it all depends what COMSOL is doing, not all solvers nor all operations are (or can be easily) parallelised.

This is often wery frustrating when you are postprocessng a very large model with very mansy DOF (as need for solving correctly i.e. in RF or optics) but then you want to postprocess and often the desired values you are looking at do not have any need for the high mesh resolution, you still have to wait for ages to run through the hughe solver DB, and that for each plot.

Ideally, you should be able to define a sub-solution by decimation or 1/100 ... and then get your plots quicker. This will typically become an issue when you group to gether data from a large cluster, you would ned to have your graphics (post)processor run also hooked up on the supercluster/farm as the RAM required will not allow you to transfer it all, and then if only 1 CPU is running you will still need ages to dump a single plot.

So powerfull multiCPU PC's is not a full "quick" solution for large EM ...
Have fun Comsoling
Ivar
Hi well COMSOL set up the problems to multiple CPU when it can, but it cannot always, if you look carfully at a solving sequence (typially a non-linear one) you will notice that often you switch between 1 and N cpus, it all depends what COMSOL is doing, not all solvers nor all operations are (or can be easily) parallelised. This is often wery frustrating when you are postprocessng a very large model with very mansy DOF (as need for solving correctly i.e. in RF or optics) but then you want to postprocess and often the desired values you are looking at do not have any need for the high mesh resolution, you still have to wait for ages to run through the hughe solver DB, and that for each plot. Ideally, you should be able to define a sub-solution by decimation or 1/100 ... and then get your plots quicker. This will typically become an issue when you group to gether data from a large cluster, you would ned to have your graphics (post)processor run also hooked up on the supercluster/farm as the RAM required will not allow you to transfer it all, and then if only 1 CPU is running you will still need ages to dump a single plot. So powerfull multiCPU PC's is not a full "quick" solution for large EM ... Have fun Comsoling Ivar

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