f A 2D Chebychev differential operator for the wave equation

This work analyses the performance of a two-dimensional Chebychev grid for solving the wave equation. The technique allows the implementation of non-periodic boundary conditions at the four boundaries of the numerical mesh. This implementation requires a special treatment of the boundary conditions based on one-dimensional characteristics. In addition, spatial grid adaptation by appropriate one-dimensional stretching transformations allows a more accurate modelling of complex media, and the reduction of the computational cost by controlling the minimum grid spacing.