On 19 Dec 2014, at 17:12, Jed Brown <j...@jedbrown.org> wrote: > Lawrence Mitchell <lawrence.mitch...@imperial.ac.uk> writes: > >> Dear petsc-users, >> >> I'm trying to setup matrices and data structures for use with >> MatGetLocalSubMatrix, but I'm rather lost in a world of ISes and block >> sizes. I have the layouts and so forth correct where all my fields have >> block size 1, but am struggling to follow how things fit together for block >> size > 1. >> >> I have a Taylor-Hood discretisation so a P2 velocity space with block size >> 2, and a P1 pressure space with block size 1. >> >> On each process, I build the full local to global mapping for both fields. >> This has block size 1. > > How are you ordering the fields on each process?
field_0_proc_0, field_1_proc_0, ..., field_N_proc_0; field_1_proc_0, ..., ...; ... field_N_proc_P > >> Then I create strided ISes to define the local blocks for each field, and >> set the block size on each of them (2 for the velocity space, 1 for the >> pressure). Aside, when I do ISCreateStride for an IS with a block size > 1, >> do I provide all the indices, or just the blocked indices? Should I be >> using ISCreateBlock for block size > 1 instead? > > ISSTRIDE has no concept of block size and can't be used to describe > blocked index sets. Use ISBLOCK instead. What is ISSetBlockSize for then? Just hanging information on the IS for use elsewhere? >> Calling MatGetLocalSubMatrix results in an error: >> >> [0]PETSC ERROR: --------------------- Error Message >> -------------------------------------------------------------- >> [0]PETSC ERROR: Petsc has generated inconsistent data >> [0]PETSC ERROR: Blocksize of localtoglobalmapping 1 must match that of >> layout 2 > > Hmm, I'm concerned that this might not work right after some recent > changes to ISLocalToGlobalMapping. Can you reproduce this with some > code I can run? I'll try and put something together. Thanks, Lawrence
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