Thanks Matt and Jed, I think I'm straight on usage/philosophy here.
A On Fri, Aug 27, 2010 at 2:42 PM, Matthew Knepley <knepley at gmail.com> wrote: > Simply, in PETSc, getFoo() and restoreFoo() operate an object pool. > > Matt > > > On Fri, Aug 27, 2010 at 11:23 AM, Jed Brown <jed at 59a2.org> wrote: > >> On Fri, 27 Aug 2010 14:13:01 +0300, Aron Ahmadia < >> aron.ahmadia at kaust.edu.sa> wrote: >> > What exactly is the purpose of these routines then? Is there a global >> > Vector associated with a DA? If so, why are the values uninitialized? >> >> It's common to need work vectors in places like residual evaluation and >> Jacobian assembly. There is a little bit of setup cost to allocate a >> new vector each time, so usually we'd prefer that they be persistent and >> just reuse them. One option would be to make the user manage this >> themselves, but that's error prone because it's easy to accidentally >> alias the work vectors, so instead the DA keeps a cache of vectors. It >> starts out empty, and each time you call DAGetGlobalVector(), the cache >> is searched for an available vector. If none are found, a new one is >> allocated and the cache grows by one. DARestoreGlobalVector() checks a >> vector back in so it may be used elsewhere. These vectors are destroyed >> in DADestroy(). >> >> Jed >> > > > > -- > 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 > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20100827/dcd73c11/attachment.html>
