Solving an elliptic equation

EllBase provides a calling interface for each of the elliptic classes implemented. As a user you must provide all information needed for a particular elliptic class. In general this will include

• the gridfunction(s) to solve for
• the coefficient matrix or source terms
• information on termination tolerances
• the name of the solver to be used

Motivation: At a later stage you might want to compile with a different solver for this elliptic class: just change the name of the solver in your elliptic interface call. If somebody improves a solver you have been using, there is no need for you to change any code on your side: the interface will hide all of that. Another advantage is that your code will compile and run, even though certain solvers are not compiled in. In this case, you will have to do some return value checking to offer alternatives.