“…4 Aside from grid adaptation strategies based on elements subdivision, see, eg, Hartmann and Leicht,5,6 or conforming grid modification, see, eg, Dolejší and Felcman, 7 an alternative approach, based on the adaptive coarsening of a fine mesh, has been proposed by Bassi et al 8 in the context of DG methods and applied by Di Pietro and Specogna to hybrid high-order formulations of electrostatics. 9 Recently, Collis and Houston also developed an agglomeration-based adaptive mesh refinement algorithm coupled with a goal-oriented error estimator applied to the DG approximation of the linear elasticity equations for a homogeneous isotropic material. 10 The adaptive coarsening strategy is attractive from the implementation viewpoint as the background mesh does not change and no nodes nor elements are dynamically added, moved, or removed.…”