“…Staggered discontinuous Galerkin (SDG) methods pioneered by Chung and Engquist [13,14] earn many desirable properties such as mass conservation, superconvergence and the flexibility to deal with general quadrilateral and polygonal meshes, and have been applied to numerous partial differential equations arising from the practical applications (cf. [15,28,17,20,16,12,38,40]). To further advance the applications of SDG method, a mortar formulation is developed for SDG method [24], where different triangulations in different regions of the computational domain are exploited.…”