[petsc-users] Sparse triangular solver

[Hoang-Vu Dang]

Hi Barry,

>  Are you free to pick whatever (parallel) data structure for the lower
and upper triangular parts you want? Or are they given to you?

Yes I am free to pick any data structure, of course it must be possible for
me to work with or be able to convert from a different format (say CSR /
COO). I do not care yet about how efficient is the conversion part.

>  Are you doing many triangular solves at the same time with different
right hand sides, or are you doing them one at a time?

My current intention is to work with one vector at a time.


On Mon, Mar 9, 2015 at 10:38 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> > On Mar 8, 2015, at 10:40 PM, Hoang-Vu Dang <dang.hvu at gmail.com> wrote:
> >
> > Sorry for causing the confusion, I should have clarify the term
> "triangular solver".
> >
> > What I mean is that I do not need a factorization from a general matrix
> to LU form.
> >
> >  I already have the matrix in lower/upper triangular form. So the solver
> is really just backward/forward substitution.
>
>   The details of the backward/forward substitution depend in great deal on
> the (parallel) data structure used to store the lower and upper triangular
> part. This is why the lower/upper triangular solvers are tied to the same
> code that does the factorization; for example I cannot factor with MUMPS
> and then do the triangular solves with SuperLU_Dist since they assume
> different and complicated (parallel) data structures.
>
>    Are you free to pick whatever (parallel) data structure for the lower
> and upper triangular parts you want? Or are they given to you? Are you
> doing many triangular solves at the same time with different right hand
> sides, or are you doing them one at a time?
>
>   Barry
>
> >
> > See here, I got the terminology from
> http://www.mcs.anl.gov/papers/P1658.pdf
> >
> > The algorithm "sparse triangular solve", unless I misunderstood the
> paper. The paper specifically mentioned PETSC so that's where I'm starting
> from.
> >
> > I hope that makes thing clearer,
> >
> > Cheers,
> > Vu
> >
> > On Sun, Mar 8, 2015 at 9:28 PM, Hong <hzhang at mcs.anl.gov> wrote:
> > Hoang-Vu :
> > If I do not need the full solver/factorization but just the backward
> subs, do i need any special treatment ? Is there a way to hint the solver
> to apply only the last step to reduce overhead ?
> >
> > What do you mean " do not need the full solver/factorization"?
> > Do you need incomplete matrix factorization, e.g., ILU, instead of full
> factorization?
> > The backward subs are steps AFTER matrix factorization.
> >
> > Hong
> >
> > On Mar 8, 2015 6:26 PM, "Barry Smith" <bsmith at mcs.anl.gov> wrote:
> >
> >   PETSc provides sparse parallel LU (and Cholesky) factorizations and
> solves via the external packages SuperLU_Dist, MUMPS, and Pastix. You need
> to first configure PETSc to use one or more of those packages for example
> ./configure --download-superlu_dist --download-metis --download-parmetis.
> >
> >   It is generally best to use the linear solvers via the PETSc KSP
> interface (even for direct solvers such as LU). So you create a KSP object,
> provide the matrix object and call KSPSolve(). You can control the solver
> used via the options database; to use the installed SuperLU_Dist you would
> use -pc_type lu -pc_factor_mat_solver_package superlu_dist
> >
> >   The MatrixMarket format is no good for parallel computing so you must
> first convert the file from MatrixMarket format to the PETSc binary format
> (see
> http://www.mcs.anl.gov/petsc/documentation/faq.html#sparse-matrix-ascii-format
> ) and then  you can use MatLoad() to load the matrix in parallel and then
> pass it to the KSP solver. For example
> src/ksp/ksp/examples/tutorials/ex10.c does this.
> >
> >
> >   Barry
> >
> > > On Mar 8, 2015, at 6:08 PM, Hoang-Vu Dang <dang.hvu at gmail.com> wrote:
> > >
> > > Hi,
> > >
> > > I would like to use petcs to perform parallel backward/forward
> substitution for sparse triangular matrices in a distributed memory cluster
> (with MPI).
> > >
> > > Could someone provide me some pointers on how to do this or whether
> petsc is good for this task ?
> > >
> > > I think there is MatSolve method, but unsure whether it supports good
> algorithm for sparse triangular matrices and how to provide an input in a
> MartrixMarket format / CSR format.
> > >
> > > Thank you
> > > Vu
> >
> >
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20150309/5e62f1c6/attachment-0001.html>