## extend solvers for a BCRSMatrix with general BlockType

Taken from !76 (merged):
discussion on how to export the istl solvers in the general case, i.e., not only for `FieldMatrix<1,1>`

.
I'm just trying to figure out how to trigger the generation of the python `solver`

module. I'm not really enough of an istl expert I guess to be sure of getting all the possible combinations right...

My suggestion was to first focus on the `IterativeSolver`

(or possibly `InverseOperator`

) for a given (square) block sized matrix. That was the idea of my final suggestion, which could also be for example implemented as

`dune.istl.solvers.cg(matrix,....)`

in both case on module exporting all the iterative solvers for the `blockSize`

associates with `matrix`

would be generated. That would be quite easy to do I think. The preconditioners could also be exported in the same module and used for example like this:

```
seqJacobi = dune.istl.preconditioners.seqJacobi(matrix)
dune.istl.solver(matrix, seqJacobi, 1e-10)
```

Although I personally don't like to double `matrix`

argument here.

Exporting a more general `LinearOperators`

would of course be of interest but I guess only if one could derive from the virtual interface on the Python side. Of course possible but that would be a further project...