Yep - we've known about this for a while. We have special preallocation routines that spew zeros into the matrix for stuff like future contact interactions before the first matassemblybegin/end.
I'm glad they made it error by default now as it can be a tricky thing to hunt down. For instance you might only test your code with small cases that run so fast you dont notice... But when you go to run a real problem everything is _dog slow_.... Derek Sent from my iPad On Mar 22, 2012, at 1:42 PM, Roy Stogner <royst...@ices.utexas.edu> wrote: > > Did you know that MatAssemblyBegin/End() wipes any > not-already-assembled entries from the matrix, forcing them to be > reallocated if they're part of a future assembly? Nice optimization > in most cases, but I wish I knew how to turn it off. > > Anyway... > > I just wasted an hour or two trying to debug such a preallocation > failure in a PETSc-linked code; in hindsight that might have been > reduced to a few minutes if only I'd known from the start that it was > a preallocation failure. > > Should we turn on MAT_NEW_NONZERO_ALLOCATION_ERR by default in our > PetscMatrix objects (at least the AIJ/BAIJ ones), either all the time > or when we're in debug/devel modes? On the one hand, I can imagine > people wanting to expand their matrices beyond the DofMap-allocated > sparsity pattern, and it seems crude to prevent that or to require > them to jump through solver-package-specific hoops first. On the > other hand, PETSc (understandably) makes such expansion *really* slow, > so anyone doing it is almost certainly making an inadvertent mistake. > --- > Roy > > ------------------------------------------------------------------------------ > This SF email is sponsosred by: > Try Windows Azure free for 90 days Click Here > http://p.sf.net/sfu/sfd2d-msazure > _______________________________________________ > Libmesh-devel mailing list > Libmesh-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/libmesh-devel ------------------------------------------------------------------------------ This SF email is sponsosred by: Try Windows Azure free for 90 days Click Here http://p.sf.net/sfu/sfd2d-msazure _______________________________________________ Libmesh-devel mailing list Libmesh-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-devel
