.BG
.FN abline
.TL
Plot Line in Intercept-Slope Form
.CS
abline(coef)
abline(a, b)
abline(reg)
abline(h=)
abline(v=)
.AG coef
vector containing the intercept `a' and slope `b' of the
line y=`a'+`b'*x.
.AG a,b
intercept and slope as above.
.AG reg
a regression object, such as returned by `lsfit'.
Specifically, `reg$coef', if it is of length 2,
will be used to define the intercept and slope of the line.
If `reg$coef' is of length 1, it is treated as
the slope of a fit through the origin.
.AG h
vector of y-coordinates for horizontal lines across plot.
.AG v
vector of x-coordinates for vertical lines across plot.
.GR
.SE
The effect of `abline' is that the line y=`a'+`b'*x
or the specified horizontal and vertical lines are drawn across the
current plot.
A warning is given if an intercept/slope line does not intersect the plot.
.EX
     # line with 0 intercept and slope 1
abline(0,1)
     # line produced by least-squares fit
abline(lsfit(longley.x[,1],longley.y))
     # dotted vertical lines at x==0 and 10
abline(v=c(0,10),lty=2)
.KW aplot
.WR
