void context (plot_number) SIMPLT.C Level 3
int plot_number  The number of the activated subplot. Numbers must start at 0 and run consecutively up to one less than the the number specified in the call to simuplot().
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.