.BG
.FN segments
.FN arrows
.TL
Plot Disconnected Line Segments or Arrows
.CS
segments(x1, y1, x2, y2)
arrows(x1, y1, x2, y2, size=.2, open=F, rel=F)
.AG x1,y1,
.AG x2,y2
coordinates of the end-points of the segments or arrows.  Lines
will be drawn from `(x1[i],y1[i])' to `(x2[i],y2[i])'.
.NA
Any segments with any `NA's as end-points will not be drawn.
.AG size
width of the arrowhead as a fraction of the length of the arrow
if `rel' is `TRUE'.
If `rel' is `FALSE', `size' is arrowhead width in inches.
.AG open
logical, if `TRUE' the arrowhead is "v" shaped, if `FALSE'
it is diamond shaped.
.AG rel
logical, should arrowhead be sized relative to the length of the
arrow?
.GR
.SA
`lines' which draws a curve (connected line
segments).
.EX
# draw arrows from `i'th to `i+1'st points
s <- seq(length(x)-1)  # sequence one shorter than x
arrows(x[s], y[s], x[s+1], y[s+1])
.KW aplot
.WR
