说明：   FDTD Finite-Difference Time-domain in free space no ABC FDTD(t) runs FDTD for time t. FDTD implements the FDTD/staggered leapfrog scheme over time 0-max_time and space 0-max_space. This program simulates a gaussian pulse in the grid specified with max_time and max_space. The pulse is sent from the center of the problem space and disperses in both directions -Kira Heater