We shall first consider plotting simple graphs showing the dependence of one variable upon another. Such a graph may be composed of several elements:
A box which defines the ranges of the variables, perhaps with axes and numeric labels along its edges.
A set of points or lines within the box showing the functional dependence.
A set of labels for the variables and a title for the graph.
In order to draw such a graph, it is necessary to call at least four of the PLplot functions:
plinit, to initialize PLplot.
plenv, to define the range and scale of the
graph, and draw labels, axes, etc.
plend, to close the plot.
More than one graph can be drawn on a single set of axes by making repeated calls to the routines listed in item 3 above. PLplot only needs to be initialized once unless plotting to multiple output devices.