Читать книгу Electromagnetic Simulation Using the FDTD Method with Python - Dennis M. Sullivan - Страница 13

Let us return to the discussion of how to determine the time step. An EM wave propagating in free space cannot go faster than the speed of light. To propagate a distance of one cell requires a minimum time of Δt = Δx/c₀. With a two‐dimensional simulation, we must allow for the propagation in the diagonal direction, which brings the requirement to . Obviously, a three‐dimensional simulation requires . This is summarized by the well‐known Courant Condition (3, 4):

(1.10)

where n is the dimension of the simulation. Unless otherwise specified, throughout this book we will determine Δt by

(1.11)

This is not necessarily the best formula; we will use it for simplicity to avoid using square roots.