[petsc-users] Parallel matrix-vector multiplication

[Gianluca Meneghello]

Hi Barry,

sorry, but I still cannot make it. I guess what I need is something similar
to MatRestrict/MatInterpolate (and B is something similar to what is
created from DMCreateInterpolation, except for the fact that the nonzero
entries are distributed differently).

Am I mistaken? Is there any example I could start from?

Thanks again,

Gianluca

On Wed, Nov 11, 2015 at 10:19 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

> DMDAGetOwnershipRanges
>
> > On Nov 11, 2015, at 10:47 PM, Gianluca Meneghello <gianmail at gmail.com>
> wrote:
> >
> > Hi,
> >
> > thanks for the very quick reply.
> >
> > One more question: is there a way to get the lx and ly from the first dm
> and use them (modified) for the second dm? DMDAGetInfo does not seem to
> provide this information.
> >
> > Thanks again for your help
> >
> > Gianluca
> >
> > On Wed, Nov 11, 2015 at 8:12 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >   When you create the 2 DM you must be set the lx, ly arguments (the
> ones you set to 0) in your code carefully to insure that the vectors for
> the 2 DM you create have compatible layout to do the matrix vector product.
> >
> >    You can run a very small problem with 2 processors and printing out
> the vectors to see the layout to make sure you get it correct.
> >
> >    The 2 DM don't have any magically way of knowing that you created
> another DMDA and want it to be compatible automatically.
> >
> >   Barry
> >
> > DMDACreate2d(PETSC_COMM_WORLD , DM_BOUNDARY_GHOSTED ,
> DM_BOUNDARY_GHOSTED , DMDA_STENCIL_BOX ,
> >       Mx      , Nx      , PETSC_DECIDE , PETSC_DECIDE , 1 , 0 , 0 , 0 ,
> &dax);
> >   DMDACreate2d(PETSC_COMM_WORLD , DM_BOUNDARY_NONE    ,
> DM_BOUNDARY_NONE    , DMDA_STENCIL_BOX ,
> >       Mx-2*bs , Nx-2*bs , PETSC_DECIDE , PETSC_DECIDE , 1 , 0 , 0 , 0 ,
> &daf);
> >
> > > On Nov 11, 2015, at 10:05 PM, Gianluca Meneghello <gianmail at gmail.com>
> wrote:
> > >
> > > Hi,
> > >
> > > I am trying to do something apparently really simple but with no
> success.
> > >
> > > I need to perform a matrix-vector multiplication x = B f , where the
> length of x is bigger than the length of f (or viceversa). Thus, B cannot
> be created using DMCreateMatrix.
> > >
> > > Both x and f are obtained from different DMs, the smaller covering
> only a subdomain of the larger. The application is to apply a control f to
> a system, e.g. \dot{x} = A x + B f.
> > >
> > > The problem is, when running on more than one core, the vector x is
> not organized as I would expect (everything works fine on a single core).
> > >
> > > I attach a short example where B is intended to map f to the interior
> of x.
> > >
> > > mpirun -n 1 ./test -draw_pause -1     works fine while
> > > mpirun -n 2 ./test -draw_pause -1     shows the problem
> > >
> > > I have not found any example with non square matrices in the src
> folder, any help is very welcome.
> > >
> > > Thanks for your time,
> > >
> > > Gianluca
> > > <test.cpp>
> >
> >
>
>
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