[petsc-users] Parallel matrix-vector multiplication

[Gianluca Meneghello]

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
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