Parameters
x in, optional numerical vector	The x values to be plotted. If omitted, then x is assumed to be channels starting at 0 and going through n_elements(y) - 1. When supplied, it must have the same number of elements as y. Unless chan is specified, this is assumed to be in the same units as the existing x axis.
y in, required numerical vector	. The y values to be plotted.

Keywords
color in, optional long integer (def. !g.oplotcolor)	The color of the line to be plotted.
chan in, optional boolean	When set, the x axis is assumed to be in channels and a conversion to the existing x axis is necessary to plot them. That conversion is done using the header information of the primary plot (the argument to the most recent show).
index out, optional variable	Returns the index associated with this oplot. This index can be used to clear this over plot using clearoplots. Note that once an index is cleared, subsequent indexes are renumbered - i.e. there are never any gaps in in index number.
idstring in, optional string	A string that can be used to identify this oplot and thereby group oplots together. This is most useful with clearoplots to remove just those oplots with the same idstring. Withing GBTIDL, all internal id strings begin with two underscores so that they are less likely to conflict with user-defined idstrings. The default is ''.