[petsc-users] grid sequencing & DMComposite

[Gideon Simpson]

There doesn’t seem to be a global analog of DMCompositeGetLocalVectors.  Do I need to do manual indexing?

-gideon

> On Sep 11, 2015, at 9:36 AM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> On Fri, Sep 11, 2015 at 8:15 AM, Gideon Simpson <gideon.simpson at gmail.com <mailto:gideon.simpson at gmail.com>> wrote:
> Ok, so here’s some behavior I don’t understand.  I am working with a DMComposite structure, and I do the following,
> 
>     SNESComputeFunction(snes,U_refine,r);
>     SNESGetDM(snes, &dm_refine);
> 
>     DMCompositeGetLocalVectors(dm_refine, &rp, &rQ);
>     DMCompositeScatter(dm_refine, r, rp, rQ);
>       
>     VecNorm(r, NORM_2, &r_norm);
>     VecNorm(rp, NORM_2, &rp_norm);
>     VecNorm(rQ, NORM_2, &rQ_norm);
> 
>     VecGetSize(r,&r_size);
>     VecGetSize(rp, &rp_size);
>     VecGetSize(rQ, &rQ_size);
> 
>     DMCompositeRestoreLocalVectors(dm_refine, &rp, &rQ);
>     VecDestroy(&r);
> 
>     PetscPrintf(PETSC_COMM_WORLD," ||r|| = %g, %i entries\n",r_norm,r_size);
>     PetscPrintf(PETSC_COMM_WORLD," ||rp|| = %g, %i entries\n",rp_norm,rp_size);
>     PetscPrintf(PETSC_COMM_WORLD," ||rQ|| = %g, %i entries\n",rQ_norm,rQ_size);
> 
> and my output is:
> 
>  ||r|| = 225.31, 7999 entries
>  ||rp|| = 140.021, 3 entries
>  ||rQ|| = 176.56, 8004 entries
> 
> 
> The arithmetic, is off, no?
> 
> I think you want Global vectors for this, not Local vectors.
> 
>   Matt
>  
> -gideon
> 
>> On Sep 10, 2015, at 5:28 PM, Barry Smith <bsmith at mcs.anl.gov <mailto:bsmith at mcs.anl.gov>> wrote:
>> 
>> 
>>  SNESGetDM()  this will return not the original DM you set but the refined one.
>> 
>>> On Sep 10, 2015, at 3:47 PM, Gideon Simpson <gideon.simpson at gmail.com <mailto:gideon.simpson at gmail.com>> wrote:
>>> 
>>> I’m using a DMCompsosite along with grid sequencing and here’s what I’m trying to accomplish.  After running the SNES solve, I’d like to evaluate the residual on the refined grid, on each piece of the DMComposite.  How do I get a DM for the refined grid which I can then use with DMCompositeGetLocalVectors in order to get each piece of the problem?  Or is there a better way?
>>> 
>>> -gideon
>>> 
>> 
> 
> 
> 
> 
> -- 
> 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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