PETSc in double-double and quad-double...

[Barry Smith]

    This is tricky because some C/C++ compilers long double uses 128  
bits of space but actually (on Intel) only uses 80 of the bits (those  
are the bits that floating point unit handles). So you do not really  
get 128 bits. Also MPI may not properly handle the 128 bit doubles.

    I am investigating qd now. Is there any MPI implementation that  
uses qd? Do you need MPI?

    Barry


On Nov 4, 2009, at 1:33 PM, Matthew Knepley wrote:

> If you are alright with EVERYTHING running with that, it already  
> works. Just set PetscScalar
> to that type. I would help you setup a configure switch for it if  
> needed.
>
> If you only want it for some operations, we would have to hear more  
> specifics.
>
>   Thanks,
>
>     Matt
>
> On Wed, Nov 4, 2009 at 10:45 AM, Todd Munson <tmunson at mcs.anl.gov>  
> wrote:
>
> Barry and Matt,
>
> I was wondering how hard it would be to modify PETSc to support  
> double-double and quad-double arithmetic using the QD package
> from LBL?
>
> Its looking more and more likely that I may need this functionality  
> for some upcoming projects that have bad scaling issues and I don't  
> want to have to reimplement KSP and PC methods...
>
> Cheers, Todd.
>
>
>
>
> -- 
> 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