... force-source included in equation (20) is located at the centre point of the computational domain, and ∂f/∂x and ∂f/∂z are set to be zero in this example and other experiments in the following section. ... 1xE , 1xE in the x-direction and 2y,1yE ,1yE in the y-direction are defined similarly. Waves in Fluids and Solids 218 3.2.1 Theoretical error Using the Taylor series ... In other words, when determining these high-order spatial derivatives included in equation (8) or equation (9), the RK method uses not only the values (a)(b) (c) Waves in Fluids and Solids...