To use the 3D Graph utility, choose the command "3D Graph" from the Utilities Menu. The menu bar will disappear, and the 3D Graph utility will fill the screen. This utility allows you to draw the graph of a function of the form z = f(x,y); the graph of such a function is a surface in three-dimensional xyz-space. By setting xmin, xmax, ymin, and ymax, you specify the rectangular region in the xy-plane for which the graph will be drawn. You must also set the values of zmin and zmax, which determine what part of the z-axis will be shown in the graph.
Actually, of course, only an approximation of the graph can be drawn. The value of the function is computed for each point in a grid of points in the xy-plane. This grid can have between 8 and 50 points along each side. (There is a text-entry box where you can specify the number of points to be used.) Each point (x,y) in this grid corresponds to a point (x,y,f(x,y)) on the graph. The picture you see is obtained by drawing lines through these points. Because this graphing method is so simple, 3D Graph will not always work well for functions that are not continuous.
There are actually four different styles in which the graph can be drawn. In the first, all the lines are drawn as described in the preceding paragraph; this is called a "wire mesh" model, and it can look rather confusing. In the second style, "hidden lines" which are behind other parts of the graph, are removed, which makes the graph look more realistic. In the other two styles, which are available only if your Macintosh has enough colors, the graph is shaded to give it an even more realistic look.
A horizontal and a vertical scroll bar are provided to allow you to control the orientation of the graph. Changing the position of the horizontal scroll will rotate the graph about the z-axis. Changing the position of the vertical scroll will "tilt" the graph towards you or away from you.
