The function plenv is used to define the scales and axes for simple
graphs. plenv starts a new picture on the next subpage (or a new
page if necessary), and defines the ranges of the variables required.
The routine will also draw a box, axes, and numeric labels if
requested.
For greater control over the size of the plots, axis labelling and
tick intervals, more complex graphs should make use of the functions
plvpor, plvasp, plvpas, plwind, plbox, and routines for
manipulating axis labelling plgxax through plszax.