[petsc-users] Assembling primal Schur matrix in FETI-DP method

[Jed Brown]

On Fri, Nov 18, 2011 at 07:53, Thomas Witkowski <
Thomas.Witkowski at tu-dresden.de> wrote:

> Defining the sparsity pattern is no problem. But is there any
> documentation on MatFDColoringApply? The online function reference is quite
> short and is not mentioned in the manuel. So, I have no real idea how this
> is related to my question.


You can find an example in snes/examples/tutorials/ex15.c

The point is that it can compute the Schur complement by coloring. In your
case, you can do subdomain solves independently, so you can compute

S = K_PiPi - K_PiB inv(K_BB) K_BPi

on each subdomain using

Tmp = inv(K_BB) K_BPi      (via MatMatSolve)

Tmp2 = K_PiB * Tmp     (via MatMatMult)

S = K_PiPi - Tmp2    (via MatAXPY)


You would then assemble the resulting independent matrices into the global
matrix.
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