A review on arbitrarily regular conforming virtual element methods for second- and higher-order elliptic partial differential equations

The virtual element method is well suited to the formulation of arbitrarily regular Galerkin approximations of elliptic partial differential equations of order 2p(1), for any integer p(1) >= 1. In fact, the virtual element paradigm provides a very effective design framework for conforming, finite dimensional subspaces of H-p2(Omega), Omega being the computational domain and p(2) >= p(1) another suitable integer number. In this review, we first present an abstract setting for such highly regular approximations and discuss the mathematical details of how we can build conforming approximation spaces with a global high-order regularity on Omega. Then, we illustrate specific examples in the case of second- and fourth-order partial differential equations, that correspond to the cases p(1) = 1 and 2, respectively. Finally, we investigate numerically the effect on the approximation properties of the conforming highly-regular method that results from different choices of the degree of continuity of the underlying virtual element spaces and how different stabilization strategies may impact on convergence.