[Fabian_W]

I have a non-regular grid.

I need to have a matrix at hand for the Laplacian operator.

I do
fvMatrix<scalar> m = fvm::laplacian(k, h);
where h seems (and shall be) irrelevant.

Now to my issue. I need to work on a subset of the nodes. Say 10 nodes are of interest.
I can set all nodes but the few special one in k to zero and get m which is zero in most coefficients.

The question is, is there a way to construct a smaller m?

One idea is, to create a smaller vector k which has only the nodes from the set and all neighbors of these nodes. Is this a good idea? How can I construct such a volScalarField?

I'm quite new to OpenFOAM, help is very much appreciated!

Fabian