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/20100827/3e5116e5/attachment.html>