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

[Thomas Witkowski]

Zitat von Jed Brown <jedbrown at mcs.anl.gov>:

> 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)

Some technical question on this point: How can I explicitly factorize  
a sequential matrix? Is MatLUFactor the correct function to do it? If  
so, how can I provide the package (i.e. umfpack) that should be used  
for factorization?

Thomas





>
> Tmp2 = K_PiB * Tmp     (via MatMatMult)
>
> S = K_PiPi - Tmp2    (via MatAXPY)
>
>
> You would then assemble the resulting independent matrices into the global
> matrix.
>