> On Mar 6, 2015, at 8:22 PM, Dmitry Karpeyev <[email protected]> wrote: > > > > On Fri, Mar 6, 2015 at 6:03 PM Barry Smith <[email protected]> wrote: > > > On Mar 6, 2015, at 4:41 PM, Jed Brown <[email protected]> wrote: > > > > Dmitry Karpeyev <[email protected]> writes: > >> This is trickier than it might appear: nonzerostate effectively counts the > >> global number of nonzeros. > > No it does not. Note in MatZeroRows_SeqAIJ() when entries are deleted from > the matrix we still increase the nonzerostate. > From MatAssemblyEnd_MPIAIJ(): > > if ((!mat->was_assembled && mode == MAT_FINAL_ASSEMBLY) || > !((Mat_SeqAIJ*)(aij->A->data))->nonew) { > PetscObjectState state = aij->A->nonzerostate + aij->B->nonzerostate;
This is ok. So long as the two sub matrix states are always increasing the state of the total matrix will increase. > ierr = > MPI_Allreduce(&state,&mat->nonzerostate,1,MPIU_INT64,MPI_SUM,PetscObjectComm((PetscObject)mat));CHKERRQ(ierr); > } > > Barring MatZeroRows MATSEQAIJ matrices aij->A and aij->B will simply > increment their nonzerostates on each new nonzero insertion in > MatSetVAlues_SeqAIJ(), so the containing MATMPIAIJ M ends up with the total > number of nonzeros in its nonzerostate. > > Now I reset my M. That will blow away aij->A and aij->B. They should not be "blown away". They should also be reset and in being reset their nonzerostate will never get smaller. > I can now insert the same number of nonzeros, but in a different pattern. M > will end up with the same nonzerostate as before the reset and confuse the > PC, no? Why are you reseting the nonzerostate to zero, just don't do that. > > This started out as a discussion about MatReset(), but I think this _may_ be > a bug we are seeing in one of the elastic contact applications: PCASM tries > to rebuild itself with MAT_REUSE_MATRIX when subdomain matrices actually have > different numbers of nonzeros. I have to say I haven't ascertained that an > inconsistent nonzerostate cases the problem, yet -- reproducible test cases > that trigger the problem are still too big to debug. It is possible that somewhere the state is not properly handled by being incremented. Barry > > >> The PC will rebuild if its state is stale, but > >> it will reuse matrices (e.g., subdomain matrices in PCASM) if nonzerostate > >> is up to date. This works if the sparsity pattern never drops nonzeros, > >> but that's no longer true if reset is allowed. I can reset a matrix, > >> preallocate and assemble it so that the global number of nonzeros will be > >> the same as before the resetting, but local sparsity patterns will change. > >> This could happen, for example, when I have moving particles or, less > >> exotically, when I have elastic contact and nodes move past each other. > >> That will break PCASM. > > Just increase the nonzerostate flag by one on a reset (that is there is no > reason to ever set it back to zero). Now nonzerostate is monotonically > increasing. > > Barry > > > Barry > > > > > On pretty simple and reliable solution would be to take a cryptographic > > hash of the row/col arrays. I assume BG is really atrocious at hashing, > > but is it so bad that this is not viable? (There are several places > > where we use kinda fragile state counters or trust the user, but hashes > > would make rebuilding more reliable and transparent.) >
