Class for multidimensional Gaussian integration rules
Empty – just establishes the template parameters.
General logic: The template parameters correspond to those of the QElement family so that the integration scheme Gauss<DIM,NNODE_1D> provides the default ("full") integration scheme for QElement<DIM,NNODE_1D>. "Full" integration means that for linear PDEs that are discretised on a uniform mesh, all integrals arising in the Galerkin weak form of the PDE are evaluated exactly. In such problems the highest-order polynomials arise from the products of the undifferentiated shape and test functions so a 4 node quad needs an integration scheme that can integrate fourth-order polynomials exactly etc.