[petsc-users] Fwd: SNES with Fieldsplit + MatNest in parallel

[Nicolas Barnafi]

Whoops, I think the notation wasn't very good, sorry. This should have 
been my previous message:

Rank-0, is_0: [0 1 2] ... [633 634 635]
Rank-0, is_1 [636 637 638] ... [729 730 731]
Rank-1, is_0: [732 733 734] ... [1368 1369 1370]
Rank-1, is_1 [1371 1372 1373] ... [1464 1465 1466]

where I am printing the three first and last elements of each IS object, 
so in fact the first processor has the range [0,635] (is0) + [636,731] 
(is1) and the second one has [732, 1370] (is0) + [1371, 1466] (is1). 
This is actually the smallest (3D) problem I have access to without 
changing anything, as I have hard-coded some elements (i.e. boundary 
conditions). It still runs super quickly, so it is not much of a problem 
to debug it as it is.

Thanks you,
NB
>
> I am now completely confused. The way PCFIELDSPLIT works, when doing 
> Schur complements, is to take
> in two ISes, which can be thought of as lists of vector rows. These 
> two ISes must partition [0, N) if N is the
> global size of the problem. So
>
>   1) The numbers you have above do not appear to be a partition
>
>   2) The problem appears to be huge. Use a problem with 2-4 to debug.
>
>   Thanks,
>
>      Matt
>
>     Thanks!
>     NB
>
>
>
>
> -- 
> 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
>
> https://www.cse.buffalo.edu/~knepley/ 
> <http://www.cse.buffalo.edu/~knepley/>

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