[petsc-users] Computing part of the inverse of a large matrix

[Matthew Knepley]

I think the easier way to do it is to use a KSP which is configured to do
preonly and LU. That will do the right thing in parallel.

   Matt

On Mon, Sep 30, 2019 at 11:47 AM Smith, Barry F. via petsc-users <
petsc-users at mcs.anl.gov> wrote:

>
>    The Python wrapper for PETSc may be missing some functionality; there
> is a manual process involved in creating new ones. You could poke around
> the petsc4py source and see how easy it would be to add more functionality
> that you need.
>
>
>
> > On Sep 30, 2019, at 10:13 AM, Jan Grießer <griesser.jan at googlemail.com>
> wrote:
> >
> > I configured PETSc with MUMPS and tested it already for the spectrum
> slicing method in Slepc4py but i have problems in setting up the LU
> factorization in the PETSc4py. Since i do not find the corresponding
> methods and commands in the source code. Thats why is was wondering if this
> is even possible in the python version.
> >
> > Am Mo., 30. Sept. 2019 um 16:57 Uhr schrieb Smith, Barry F. <
> bsmith at mcs.anl.gov>:
> >
> >   If you want a parallal LU (and hence the ability to build the inverse
> in parallel) you need to configure PETSc with --download-mumps
> --download-scalapack
> >
> >   Barry
> >
> >
> > > On Sep 30, 2019, at 9:44 AM, Jan Grießer <griesser.jan at googlemail.com>
> wrote:
> > >
> > > Is the MatMumpsGetInverse also wrapped to the python version in
> PETSc4py ? If yes is there any example for using it ?
> > > My other question is related to the LU factoriation (
> https://www.mcs.anl.gov/petsc/documentation/faq.html#invertmatrix).
> > > Is the LU factorization only possible for sequential Aij matrices ? I
> read in the docs that this is the case for ordering.
> > > After setting up my matrix A, B and x i tried:
> > >  r, c = dynamical_matrix_nn.getOrdering("nd")
> > >  fac_dyn_matrix = dynamical_matrix_nn.factorLU(r,c)
> > >
> > > resulting in an error:
> > > [0] No support for this operation for this object type
> > > [0] Mat type mpiaij
> > >
> > > Am Fr., 27. Sept. 2019 um 16:26 Uhr schrieb Zhang, Hong <
> hzhang at mcs.anl.gov>:
> > > See ~petsc/src/mat/examples/tests/ex214.c on how to compute selected
> entries of inv(A) using mumps.
> > > Hong
> > >
> > > On Fri, Sep 27, 2019 at 8:04 AM Smith, Barry F. via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> > >
> > > MatMumpsGetInverse() maybe useful. Also simply using MatMatSolve()
> with the first 1000 columns of the identity and "throwing away" the part
> you don't need may be most effective.
> > >
> > >    Barry
> > >
> > >
> > >
> > > > On Sep 27, 2019, at 3:34 AM, Jan Grießer via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> > > >
> > > > Hi all,
> > > > i am using petsc4py. I am dealing with rather large sparse matrices
> up to 600kx600k and i am interested in calculating a part of the inverse of
> the matrix(I know it will be a dense matrix). Due to the nature of my
> problem, I am only interested in approximately the first 1000 rows and 1000
> columns (i.e. a large block in the upper left ofthe matrix).  Before I
> start to play around now, I wanted to ask if there is a clever way to
> tackle this kind of problem in PETSc in principle. For any input I would be
> very grateful!
> > > > Greetings Jan
> > >
> >
>
>

-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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