|Call context() to change the active page and/or axes region
when plotting. The argument indicates which plot region to use for future
GraphiC calls. context() maintains track of the current defaults
for each subplot, e.g., the line style, thickness, color, etc. See FERMI.C.
for an example of how to use this feature.
The context() function can be used to overlay plots so that they
can share the same plot space but use multiple axes. An example of this
is in the program MULTI_Y.C in the examples section.