# Conceptual Overview

Consider the plot and model structure shown in Figure 13-1. The plot shows the idealized behavior of a real-world system - in this case, the temperature of a cooling cup of coffee. The model is idealized as well - if it was solved analytically, it would yield exactly the behavior exhibited by the plot.

When the computer is used to simulate systems such as this, it is not possible to get an exact solution. Instead, a set of discrete calculations (the only kind that digital computers are capable of producing) is used to approximate the idealized curve. The software divides the time axis into equally-spaced intervals, each with a width of DT (or "delta time"). Then, calculations are performed at discrete intervals, as indicated in Figure 13-2.

Figure 13-1 Idealized Behavior of Cooling Model

Figure 13-2 Simulated Behavior of Cooling Model