Implementation of $hp$-adaptive discontinuous finite element methods in Dune-Fem

In this paper we describe generic algorithms and data structures for the implementation of $hp$-adaptive discontinuous finite element methods in the Dune-Fem library. Special attention is given to the often tedious and error-prone task of transferring user data during adaptation. Simultaneously, we generalize the approach to the restriction and prolongation of data currently implemented in Dune-Fem to the case of $p$- and $hp$-adaptation. The dune-fem-hpdg module described in this paper provides an extensible reference implementation of $hp$-adaptive discontinuous discrete function spaces. We give details on its implementation and the extended adaptive interface. As proof of concept we present the practical realization of an $hp$-adaptive interior penalty method for elliptic problems.