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3.1.1 plg
Yorick's plg command plots a one dimensional array of y values
as a function of a corresponding array of x values. To be more
precise,
plots a sequence of line segments from (x(1),y(1)) to
(x(2),y(2)) to (x(3),y(3)), and so on until
(x(N),y(N)), when x and y are N element arrays.
The "backwards" order of the arguments to plg (y,x instead of x,y)
allows for a default value of x. Namely,
plots y against 1, 2, 3, ..., N, or indgen(numberof(y)) in Yorick
parlance. You often want a plot of an array y with the horizontal
axis (y is plotted vertically) merely indicating the sequence of
values in the array.
Optional keyword arguments adjust line type (solid, dashed, etc.), line
color, markers placed along the line, whether to connect the last point
to the first to make a closed polygon, whether to draw direction arrows,
and other variations on the basic connectthedots theme.
Specifying line type 0 or "none" by means of the type= keyword causes
plg to plot markers at the points themselves, rather than a polyline
connecting the points. Here is how you make a "scatter plot":
For a polymarker plot, x and y may be scalars or unit length arrays. If
you need to specify your own marker shapes (perhaps to plot experimental
data points), you may want to use the plmk function  use the help
function to find out how.
