Before revision:  In discontinuous Galerkin time-domain (DGTD) methods, assigning smooth-varying coefficients calls for storing individual mass matrices for each mesh element , which significantly increases the memory-cost. This workproposes a memory-efficient implementation of smooth-varying PMLs in DGTD. A weight-adjusted approximation is applied to the mass matricesinvolved in the PML formulation, which yields a low memory-cost algorithm and maintains the high-order accuracy of DGTD.
After revision:  In discontinuous Galerkin time-domain (DGTD) methods, assigning smooth-varying coefficients calls for storing individual mass matrices for each mesh element , which significantly increases the memory footprint. In this work, this bottleneck is addressed by applying a weight-adjusted approximation is applied to the mass matricesinvolved in the PML formulation, which yields a low memory-cost algorithm and maintains the high-order accuracy of DGTD.