arrows(x0, y0, x1, y1, length=0.25, angle=30,
code=2, col, lty)
(x0[i], y0[i])
and the point (x1[i],y1[i]). length gives the length of the
edges of the arrow head (in inches) and angle specifies the angle
from the shaft of the arrow to the edge of the arrow head. If
code=2 an arrowhead is drawn at (x0[i],y0[i]) and if
code=1 an arrowhead is drawn at (x1[i],y1[i]). If
code=3 a head is drawn at both ends of the arrow.
The graphical parameters col and lty can be used
to specify a color an line texture for the line segments which
make up the arrows (col may be a vector).