[petsc-dev] Error with ML preconditioner

[Jed Brown]

On Mon, Feb 18, 2013 at 3:00 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

>
> Even in Barry's original code, I don't understand why we can expect this
> check to be producing a collective result. Surely there can be some ranks
> that see everything evenly divide and others that do not.
>
> It seems to me that we should either (a) explicitly disallow matrices with
> a block size to be built when the blocks are not filled or (b) when the
> user requests blocks, pad blocks so that we can always use an ISBlock.
>

It shouldn't be hard to build a test that will expose this problem. Just
declare a block size (2), then assemble a matrix that does not fill out the
block size. In the off-diagonal part of rank 0, we should have one full
block, while in the off-diagonal part of rank 1, we should have anything
that isn't a perfect block.
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