Example of nodal DG elements in a computational domain in ﹩{\mathbb{R}}\times {{\mathbb{R}}}^{+}﹩. Figure 2(a) shows the interpolation points ﹩\{{\xi }_{j}^{i}\}{}_{j=1}^{{N}_{{\boldsymbol{x}}}}﹩ and ﹩\{{\xi }_{j}^{\varepsilon }\}{}_{j=1}^{{N}_{\varepsilon }}﹩ in a nodal DG element K in the local coordinate. Figure 2(b) shows the union ﹩{ \mathcal K }﹩ of all elements K and the space and energy nodes—the values of the interpolation points in the global coordinate. Figure 2(b) also illustrates the collection of space nodes S_x and the collection energy nodes S_ε, which are defined in Equations (40) and (41).