Before revision:  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:  The proposed scheme has the same advantages as the scheme that stores individual mass matrices, namely higher accuracy (due to reduced numerical reflection) and increased meshing flexibility (since the PML does not have to be defined layer by layer) but it requires significantly less memory .