On Mon, Feb 6, 2012 at 1:23 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> > On Feb 6, 2012, at 1:14 PM, Matthew Knepley wrote: > > > On Mon, Feb 6, 2012 at 1:11 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > > > On Feb 6, 2012, at 12:47 PM, Jed Brown wrote: > > > > > On Mon, Feb 6, 2012 at 21:42, Matthew Knepley <knepley at gmail.com> > wrote: > > > I don't like this because it would mean calling VecSetUp() all over > the place. Couldn't the ghosting flag be on the same > > > level as the sizes? > > > > > > Maybe VecSetUp() is wrong because that would imply collective. This > memory allocation is simple and need not be collective. > > > > > > Ghosting information is an array, so placing it in VecSetSizes() would > seem unnatural to me. I wouldn't really want > VecSetGhosts(Vec,PetscInt,const PetscInt*) to be order-dependent with > respect to VecSetType(), but maybe the VecSetUp() would be too messy. > > > > Only some vectors support ghosting, so the usual PETSc way (like with > KSPGMRESRestart()) is to calling the specific setting routines ONLY AFTER > the type has been set. Otherwise all kinds of oddball type specific stuff > needs to be cached in the object and then pulled out later; possible but is > that desirable? Who decides what can be set before the type and what can be > set after? Having a single rule, anything appropriate for a subset of the > types must be set after the type is set is a nice simple model. > > > > On the other hand you could argue that ALL vector types should support > ghosting as a natural thing (with sequential vectors just have 0 length > ghosts conceptually) then it would be desirable to allow setting the ghost > information in any ordering. > > > > I will argue this. > > Ok, then just like VecSetSizes() we stash this information if given > before the type is set and use it when the type is set. However if it is > set after the type is set (and after the sizes are set) then we need to > destroy the old datastructure and build a new one which means messier code. > By instead actually allocating the data structure at VecSetUp() the code > is cleaner because we never need to take down and rebuild a data structure > and yet order doesn't matter. Users WILL need to call VecSetUp() before > VecSetValues() and possibly a few other things like they do with Mat now. We just disallow setting it after the type, just like sizes. I don't see the argument against this. Matt > > Barry > > > > > Sadly we now pretty much require MatSetUp() or a > MatXXXSetPreallocation() to be called so why not always have VecSetUp() > always called? > > > > Because I don't think we need it and it is snother layer of complication > for the user and us. I think > > we could make it work where it was called automatically when necessary, > but that adds another > > headache for maintenance and extension. > > > > Matt > > > > We have not converged yet, > > > > Barry > > > > > > > > > > > > -- > > 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 > > -- 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/20120206/9bca81f0/attachment.html>