Before revision:  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. The proposed scheme has the same accuracy as the implementation of storing local mass matricesof each element, and provides a higher mesh flexibility and a smaller reflectionthan using a constant coefficient in each element .
After revision:  A weight-adjusted approximation to these mass matrices. The resulting DGTD scheme has the same accuracy as the implementation of storing local mass matricesof each element, and provides a higher mesh flexibility and a smaller reflectionthan using a constant coefficient in each element .