ABSTRACT
Propagation problems may be unsteady time (i.e., t) marching problems or steady space (i.e., x) marching problems. The marching direction in a steady space marching problem is sometimes called the time-like direction, and the corresponding coordinate is called the time-like coordinate. Figure 11.3 illustrates the open solution domains D(t) and D(x) associated with time marching and space marching propagation problems, respectively.
