On Feb 6, 2012, at 1:42 PM, Dmitry Karpeev wrote:
>
>
> On Mon, Feb 6, 2012 at 1:30 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
> On Feb 6, 2012, at 1:27 PM, Matthew Knepley wrote:
>
> > 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.
>
> We allow setting the sizes after the type.
>
> Since we are on a related subject: should then all type-specific processing
> of sizes be moved out of MatSetSizes()
> into MatSetUp? By this I mean this code:
> if (A->ops->setsizes) {
> /* Since this will not be set until the type has been set, this will NOT
> be called on the initial
> call of MatSetSizes() (which must be called BEFORE MatSetType() */
> ierr = (*A->ops->setsizes)(A,m,n,M,N);CHKERRQ(ierr);
> } else {
>
> This eliminates the need to check for the presence of various type-specific
> setup methods -- they will all be called in MatSetUp after the type is
> guaranteed to have been set. This would also make MatSetSizes not
> collective. I imagine that Vec could be organized the same way. I actually
> would prefer VecSetUp to explicitly delineate the end of the "factory" phase.
The only Mat one is MatSetSizes_SeqDense() which could be easily nuked
(someone please check my reasoning) and then the whole concept of (*setsizes)()
be removed for Mat?
Barry
>
> Dmitry.
>
>
> >
> > 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
>
>
