A general framework for solving differential equations

Recently, the efficient numerical solution of Hamiltonian problems has been tackled by defining the class of energy-conserving Runge- Kutta methods named Hamiltonian Boundary Value Methods (HBVMs). Their derivation relies on the expansion of the vector field along a suitable orthonormal basis. Interestingly, this approach can be extended to cope with more general differential problems. In this paper we sketch this fact, by considering some relevant examples.