On Sun, May 6, 2012 at 7:15 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
> Matt introduced this concept, he says the IS is a better place to attach > things. > > http://petsc.cs.iit.edu/petsc/petsc-dev/rev/2ad289ac99e0 > > I don't understand why the IS is better (because it's mostly immutable?). > I'm worried that putting it there is going to be fragile because the near > null space is not a property of an IS at all. > Its not a property of your matrix either, or you would not need me to tell you. Its a property of the operator. The operator is defined by the DM. The near null space is actually a property of a suboperator, defined by the DM using a field (we are not allowing arbitrary divisions). The representation of a field in PETSc is an IS ( http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/DM/DMCreateFieldIS.html) so it makes sense to attach field information to the IS. Moreover, it makes a hell of a lat more sense to attach an auxiliary operator (like L_p) to this IS than to a matrix. Furthermore, this scheme is completely workable in a nested context. The user can specify the IS, or pull out the DM IS and play with it, without a bunch of cumbersome copies hanging around that we do not want and can't destroy. That is what would happen with persistent submatrices. Lastly, I am running this for PyLith and it works great. Matt -- 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/20120506/bc2840ad/attachment.html>