[petsc-users] MATNEST with shell matrices

[Boyce Griffith]

On 2/21/13 7:11 PM, Jed Brown wrote:
>
> On Thu, Feb 21, 2013 at 6:07 PM, Boyce Griffith <griffith at cims.nyu.edu
> <mailto:griffith at cims.nyu.edu>> wrote:
>
>
>     Yes there is a local and global size.  They are both 0.  :-)
>
>
>
> Heh, interesting. Most finite-dimensional vector spaces have a
> dimension. May as well use VecNestGetSubVec() when needed. I don't think
> there is any code that will short-circuit in the zero-size case, but I'd
> still encourage you to state a dimension that's not obviously bogus.

For better or for worse, the "size" of the wrapped data can change 
dynamically.  Somehow it seems less dishonest to set the size to 0 
instead of, e.g., 1.  At least when you get 0 you know that the size is 
bogus!  :-)  We've been using this stuff for ... a while now, and it 
hasn't caused any problems.

That said, I would prefer to have tighter integration with PETSc.  I 
think that DMComposite is what I was thinking might work.

-- Boyce