[petsc-dev] ASM request

Barry Smith bsmith at mcs.anl.gov
Tue Mar 16 12:51:53 CDT 2010

On Mar 16, 2010, at 11:28 AM, Matthew Knepley wrote:

> There is a request to make a more memory efficient version of ASM  
> for running
> very large system of equations. They are using LU on small diagonal  
> blocks, and
> have asked that the blocks be factored, applied, and discarded,  
> rather than being
> saved for all iterations. Does anyone think this is easy in the  
> current ASM code?
> Have an alternate proposal?

    I need a better understanding. Is it that after the KSPSolve()  
they want more memory available for their own use that they will  
allocate after the KSPSolve and free before the next PCSetUp()?  If  
this is what they want then I think it is trivial to implement, but we  
will need an API so that they can say when they are done with the  
solves and want us to free up the memory.

   Normally ASM is memory intense because
1) it makes copies of the matrix subblocks
2) it factors those subblocks into additional memory.

If you use ILU(0) and the inplace option then it only needs one copy  
of the blocks instead of the two.


>    Matt
> -- 
> 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

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