[petsc-users] Fwd: ASM Index Sets Question

[Matthew Knepley]

On Wed, Mar 23, 2016 at 9:30 AM, Justin Droba (JSC-EG3) [JETS] <
justin.c.droba at nasa.gov> wrote:

> Dear all,
>
> SORRY ABOUT THE LAST MESSAGE! Hit send before I meant to!
>
> Thank you for maintaining this wonderful software and this user mailing
> list!
>
> I am attempting to use an additive Schwartz preconditioner with multiple
> blocks per processor.  I've been able to get it to work with one block per
> processor but not been successful with multiple. I believe I am not
> understanding correctly the construction of index sets for this case.
>
> Let's consider a simple example: 16 nodes on a square with 4 blocks of 4x4:
>
> [image: Image]
>
>
> I want to put [image: $\Omega_1$] and [image: $\Omega_2$] on processor 1
> and the other two on the second processor.  Do I make my index sets on
> processor 1
>
> IS = {  {1,2,3,5,6,7,9,10,11}, {2,3,4,6,7,8,10,11,12} }
> IS_LOCAL = { {1,2,5,6}, {3,4,7,8} }
>
> and similarly for the other processor?  I tried this and it isn't quite
> working out.  Do I misunderstand something?
>

That looks right to me, but you could also just use

  -pc_asm_blocks 4

unless you need fine control over how the blocks are divided.

  Thanks,

     Matt


> Thank you!
>
> Best regards,
> Justin
>
> --
> ---------------------------------------------
> Justin Droba, PhD
> Applied Aeroscience and CFD Branch (EG3)
> NASA Lyndon B. Johnson Space Center
> JETS/Jacobs Technology, Inc. and HX5, LLC
>
> *Office:* Building 16, Room 142
> *Phone*: 281-483-1451
> ---------------------------------------------
>
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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