“…The concept of weak derivatives makes WG a widely applicable numerical technique for a large variety of of PDEs arising from the mathematical modeling of practical problems in science and engineering. There is an abundant literature on such PDEs; see, e.g., elliptic equation [18,20,21,22,27,36,37,39], parabolic equation [19,42,43,45], system of equations [23,25,26,28,29,31,35,40,44], interface problems [17,30,32]. One close relative of the WG finite element method is the hybridizable discontinuous Galerkin (HDG) method [10].…”