Commit 6d280aab authored by Carsten Gräser's avatar Carsten Gräser

[!207] Improve poisson-pq2 example

Merge branch 'feature/improve-poisson-pq2-example' into 'master'

ref:staging/dune-functions This introduces several improvements to the
poisson-pq2 example:

-   Demonstrate usage of mixed grids if UGGrid is available. While there's no
    reason to use a mixed grid here, we should imho demonstrate that it simply
    works. This is done conditionally using HAVE_UG. However, we strictly
    speaking already depend on dune-uggrid, because it's used unconditionally
    in the tests.
-   Use symmetrized approach to incorporate Dirichlet data. While CG works on
    the non-symmetric approach to (because it stays in an appropriate
    subspace) it's unclear if this is still the case in the presence of a
    preconditioner (see below).
-   Use ILDL instead of ILU preconditioner. Since we use CG, the
    preconditioner should be s.p.d.. In fact it turnes out that ILDL and ILU
    generate exactly the same results once the problem is symmetrized (see
    above). However, we should still use ILDL since the ILU documentation does
    not guarantee this.
-   It turnes out that using ILDL/ILU for the properly symmetrized problem is
    much better that the old method (which was beyond any theory anyway).

See merge request [!207]

  [!207]: gitlab.dune-project.org/staging/dune-functions/merge_requests/207
parents 5b648c11 bae7ec27
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