[petsc-users] about ksp

[Likun Tan]

Instead of solving Ax=b with different right-hand-side sequentially, we
can also form a sparse block diagonal matrix A and a vector b composed of
all the elements. Then we can set values to each section of b concurrently
and solve the enlarged system in parallel, is this an efficient way?

And also, I found MatCreateMPIBDiag() is used to define a sparse block
diagonal matrix, in my case, each block has the same format and elements,
how could i set values efficiently?

Thanks,
Likun


On Mon, August 29, 2011 11:14 am, Jed Brown wrote:
> On Mon, Aug 29, 2011 at 10:08, Matthew Knepley <knepley at gmail.com> wrote:
>
>
>> As I said, no one knows
>> how to do this for Krylov methods (and everyone has tried).
>>
>
> There are methods and even simply running multiple independent Krylov
> solves concurrently would be good for memory traffic (matrix entries get
> reused for multiple vectors). The problem with block Krylov methods (that
> try to share information between multiple simultaneous solves) is loss of
> orthogonality between the subspaces generated by each vector. And it's not
> so much that there are no ways to detect and account for this, but
> robustness is still a problem and making efficient software for it is more
> tricky and AFAIK, has not been done.
>