pllab may be called after
plenv to write labels on
the x and y axes, and at the top of the picture. All the variables
are character variables or constants. Trailing spaces are removed
and the label is centered in the appropriate field. The syntax for
More complex labels can be drawn using the function
discussion of writing text in a plot see the Section called Writing Text on a Graph, and
for more detailed discussion about label generation see the Section called Writing Text on a Graph.