When calling CHOLMOD to compute the Cholesky factor of a matrix,
it was not tested whether such a factor already existed. As a
consequence, if the solver was called twice in a row, the old
factor would be lost to a memory leak.

Fix this by explicitly deallocating the old Cholesky factor
before asking CHOLMOD for a new one.

getMatOrThrow handed out a reference to the underlying matrix, but for
the compiler it was undecidable, whether this might be a dangling
refernce. This lead to many warnings. We now hand out the
AssebledLinearOperator and call getmat explicitly where ever needed.

So far doxygen did not process this file since
`HAVE_SUITESPARSE_CHOLMOD` was missing.
This also adds the missing editor hints.

CHOLMOD supports this, it just wasn't exposed in the interface.
It is needed for large problems.

See https://reuse.software/ for a description.

This is needed for some of the more advanced features of CHOLMOD.

This is achieved by using the flat matrix and vector forEach implementations.
The unit test is extended by a multi type example.

This allows other implementations which are using the istl-cholmod wrapper
to set options and other paramters of the cholmod solver

with LoopSIMD

solver or preconditioner

[solverfactory] more includes

It can happen that we work on a 0 times 0 matrix due to ignore fields or other reasons.
This leads to undefined behavior in the cholmod lib.

We simply catch this case by introducing a bool value.

We interpret Cholmod as an InverseOperator between BlockVectors. Therefore
we dump the BCRSMatrix template.

To clarify the usage of ignore nodes the apply() method now ignores the corresponding entries directly.
The information is stored in a mapping from all indices to the not ignored indices.

Also, the unit tests for cholmod are extended.

* Avoid a sign/unsigned comparison warning
* Don't use C's unqualifies size_t
* Use std::size_t in 0,...,k-1 loop

Patrick Jaap authored 6 years ago and Christoph Grüninger committed 6 years ago

A simple implementation for the SuiteSparse CHOLMOD solver for real valued
(double) linear systems.
Ignore dof's are supported.
The user has to take care of the correct size of
vectors in the "apply" method.