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Decomposition Methods: which ones are best for large scale simulations?

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Old   January 7, 2010, 13:03
Default Decomposition Methods: which ones are best for large scale simulations?
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What decomposition method (Metis, Scotch, simple, hierarchical) you guys favor for large scaled simulations?
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Old   January 8, 2010, 03:22
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Quote:
Originally Posted by misakagan View Post
What decomposition method (Metis, Scotch, simple, hierarchical) you guys favor for large scaled simulations?
Metis or scotch is what we use, since we generally don't have a better idea ourselves of how to decompose the domain any better (nor the time to figure it out anew for each geometry / cpu count combination).

Simply try out metis/scotch and see if you are happy with the results. You can view the separate processor* domains in paraview (eg, via paraFoam) to see if it matches up with your expectations.

BTW: I believe that future versions of OpenFOAM might be switching to scotch instead of metis due to licensing aspects. I found that the scotch decomposition was fairly similar to metis anyhow.
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Old   January 8, 2010, 05:35
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Quote:
Originally Posted by olesen View Post
BTW: I believe that future versions of OpenFOAM might be switching to scotch instead of metis due to licensing aspects. I found that the scotch decomposition was fairly similar to metis anyhow.
Regarding licensing I think you may use Metis from 1.5 for testing purposes only. Otherwise, you need to have a license for that. Afaik this is the main reason why it changed to scotch in 1.6.
What I miss is a parallel partitioning method freeing us from the need to have machines with very large memory.

Regards
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Old   January 8, 2010, 05:38
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Hi.

I'm using also scotch or metis since they do not require any manual input. I checked the subdomains in paraview and they seem to be convenient. But the problem is that I get a terrible speed-up (scaling) if I increase the processor number. In other words, nearly all computational effort is invested on solving the pressure-poisson equation in PISO loop, which does not scale well with increased processor number.

Are you satisfied with parallelisation of OpenFOAM? I'm asking because considering this computational performance I can not simulate anything big. Maybe I'm doing something wrong.
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Old   January 8, 2010, 05:58
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Originally Posted by bastil View Post
Regarding licensing I think you may use Metis from 1.5 for testing purposes only. Otherwise, you need to have a license for that.
Here https://projects.coin-or.org/BuildTo...Metis?rev=1294 it states
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For commercial-use, the essential restriction is for the vendors not to be reselling Metis.
The restriction appears to apply to the vendor, not the end-user - http://glaros.dtc.umn.edu/gkhome/met...faq#distribute

Last edited by olesen; January 8, 2010 at 06:07. Reason: added reference to faq
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Old   October 29, 2015, 07:13
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HI Mark,

can you please tell me how to load the separate processor domains into ParaView?

Best regards,

Kate
Quote:
Originally Posted by olesen View Post
Metis or scotch is what we use, since we generally don't have a better idea ourselves of how to decompose the domain any better (nor the time to figure it out anew for each geometry / cpu count combination).

Simply try out metis/scotch and see if you are happy with the results. You can view the separate processor* domains in paraview (eg, via paraFoam) to see if it matches up with your expectations.

BTW: I believe that future versions of OpenFOAM might be switching to scotch instead of metis due to licensing aspects. I found that the scotch decomposition was fairly similar to metis anyhow.
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Old   October 29, 2015, 10:00
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Nothing special is needed Kate. From within each processor file make the
VTK conversion, then open Paraview and load as you normally would.
Does this help?
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Old   October 29, 2015, 11:41
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Sorry, somehow I overlooked the constant directory in the processor files.

Have a nice day,

Kate
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