[petsc-users] Tensor product as matrix free method

Jed Brown jed at jedbrown.org
Tue Apr 1 09:57:04 CDT 2014

Mathis Friesdorf <mathisfriesdorf at gmail.com> writes:

> Thanks Jed, this is great. I was trying to implement what was proposed in
> http://lists.mcs.anl.gov/pipermail/petsc-users/2011-September/009991.html,
> by you as I just realised. For this the matrices would be of varying size,
> so for three local systems, I would need:
> S \otimes Id \otimes Id ; Id \otimes S \otimes Id ; Id \otimes Id \otimes S.
> Realistic systems are of the order of at least 20 local systems, which
> would mean that I need the matrices of the above structure for all 20
> possible positions.

This is something for which you should use CTF or TCE.  When S moves out
of the last position in the tensor product, the operation becomes less
local and various forms of transposition is needed.  This is not
something worth recreating in PETSc unless there is a critical
deficiency in the available libraries.
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