Definition of intergrid transfer operators in own classes to flexibly pass these operators as template arguments for multigrid solver
Currently all prolongation and restict operators are implemented in the corresponding P?Function.hpp and PrimiveDoFFunction.hpp. At a later stage, one might want to flexibly pass these transfer operators to the MultigridSolver as template argument. Therefore it might be useful to specifically design own classes for these operators. Another advantage would be that the functions can be moved outside the different (already quite long) functionSpace and DoFFunction files.