On Feb 6, 2012, at 1:39 PM, Matthew Knepley 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. > > Okay, so the current semantics are: VecSetSizes() wipes out the old Vec and > creates one of the right size.
No, if the vector has already been built then VecSetSizes() errors out; it does not build a vector of the new size. If the vector type has been set but the sizes not set then VecSetSizes() triggers actually building the data structures. Barry > I am fine > with that, and would just add a ghost size. I don't think this complicates > what is already there much at all. > > Matt > > > > > > 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 > > > > > -- > 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
