[petsc-dev] -ksp_view_binary with DA vectors

[Barry Smith]

On Jun 22, 2010, at 4:21 PM, Jed Brown wrote:

> On Tue, 22 Jun 2010 11:30:47 -0500, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>    Actually we should add the same support for matrices and then the inconsistency would disappear.
> 
> Is this actually useful?

   Saving sparse matrices to disk and reading them back in is NEVER useful except

>  I.e. would anyone actually want to work with
> the matrix in natural ordering?  If you read it in parallel, you'll get
> "slabs" instead of blocks".  If you have a different number of processes
> than you started with, the old blocks at least provide a quasi-sensible
> partition.  Even if you read it in serial, the standard partition should
> still have better memory locality.
> 
> But perhaps the issue is not performance, but just being able to easily
> compare matrices assembled on a different number of processes.

    for this kind of thing.

>  That
> does seem useful, but it seems like a fairly involved thing to
> implement.  I think I'd rather just put 1:N in the vector (in the
> natural ordering) and apply that permutation from Matlab.
> 

    Actually it is  easy. Use a MatGetSubMatrix() with an index set defined by the natural ordering and then MatView() that matrix. Trivial to implement, pretty much the same as is done for Vecs.

   Barry


> Jed