Hi everyone!

I'm a little confused about the classes that concern the development of coupled solvers.

There exist e.g. a coupledLduMatrix class and a BlockLduMatrix class. Intuitively I would say that they were conceived to do more or less the same thing, right?
As the 2 blockCoupledSolvers that are available right now use latter class, I wonder what the former is good for?
As the VectorN classes are yet outside src/OpenFOAM®/primitives I wonder in which direction the development of these classes will go. The very useful blockMatrixTools, for example, are even located inside the application section. Are they going to be part of the actual src or is the development of these parts yet not "mature" enough to put them there?

I know these are quite some questions, written in a very unordered way, but maybe somebody can just give me a short insight on how those classes are thought to evolve in the near future.

Thanks,
Michi

Hi Michi,
You are right that both classes provide similar functionality, however the approach is very different in each case so each has very specific applications.
coupledLduMatrix solves a set of matrix equations that do not necessarily share the same mesh, so it is typically used for multi-region simulations. Typical examples are conjugate heat transfer problems where solid and fluid components exchange energy at boundaries. The coupling coefficients are provided through so-called coupled interfaces. This approach assumes that the inter-equation coupling is relatively loose.
The blockLduMatrix class solves a set of coupled equations that share the same mesh and where the inter-equation coupling is stiff. So for N coupled equations the solver is actually performing NxN tensor inversions during the solution process. This is useful for modeling chemical reactions and similar processes.
So depending of the physics and meshing of your model you should choose whichever one suites you.

Thank you for the fast response Ivor! That makes everything much clearer for me.