[petsc-users] Petsc with mumps single precision

[Sylvain Mercier]

Thank you Barry for your comments,

So if you're ok with this, I'll work on it and I'll propose you a
contribution later.

Sylvain


2014-08-25 20:02 GMT+02:00 Barry Smith <bsmith at mcs.anl.gov>:

>
> On Aug 25, 2014, at 9:59 AM, Sylvain Mercier <sylvainmercier85 at gmail.com>
> wrote:
>
> > Thank you Matthew and Hong.
> >
> > That's too bad...
> > I was wondering if it would be possible to add this alternative only in
> the MUMPS interface.
> > Indeed, in the field of solid mechanics (where 3D, beams and shell are
> often mixed thanks to Lagrange multipliers), it's very usefull to factorize
> a matrix in single precision thanks to MUMPS, and use it to precondition a
> sequence of systems solved in double precision. It turns to be very robust
> and quite fast.
> >
> > In  src/mat/impls/aij/mpi/mumps/mumps.c, a new type, say
> PetscMumpsSingleScalar, could be defined in order to pass the required
> information to the single precision
> > MUMPS solver.
> >
> > Would the Petsc team accept to integrate such a feature?
>
>    Sylvain,
>
>    Yes this would be possible; it is the maintenance and clarity of the
> code that becomes an issue.  Basically all the MatConvertToTriples()
> routines would need to optionally make a copy of the numerical values into
> single precision and similarly the right hand side would need to do the
> same when some option on the factorization saying to use single precision
> is set.
>
>    Barry
>
>
>
> >
> > Thanks,
> > Sylvain
> >
> >
> > 2014-08-20 17:57 GMT+02:00 Matthew Knepley <knepley at gmail.com>:
> > On Wed, Aug 20, 2014 at 7:53 AM, Sylvain Mercier <
> sylvainmercier85 at gmail.com> wrote:
> > Hi everyone,
> >
> > I'm using PETSc to solve saddle point systems. I have found a block
> preconditionner which requires to solve a smaller symmetric positive
> definite system. I do it with  MUMPS which is fast an robust.
> > However, I would like to use this solver in single precision in order to
> compare the performances.
> >
> > So is it possible to use MUMPS in single precision inside a double
> precision solving with PETSc?
> >
> > No, right now PETSc must have all the same precision. We have
> investigated several methods for
> > using multi-precision, but none has satisfied all our needs.
> >
> >   Thanks,
> >
> >      Matt
> >
> > Thanks,
> > Sylvain
> >
> >
> >
> > --
> > 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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