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.
One or more calls to plline or plpoin to draw lines or points
as needed. Other more complex routines include plbin and
plhist to draw histograms, plerrx and plerry to draw
error-bars.
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.