abline(a, b, ...) abline(h=, ...) abline(v=, ...) abline(coef, ...) abline(reg, ...)
abline
can be used to add one or more straight lines to a plot.
The first form above specifies the line in intercept/slope
form (alternatively a can be specified on its own and is taken
to contain the slope and intercept in vector form).
The h= and v= forms draw horizontal and vertical lines
at the specified coordinates.
The coef form specifies the line by a vector containing
the slope and intercept.
reg is a regression object which contains reg$coef.
If it is of length 1 then the value is taken to be the slope of a
line through the origin, otherwise, the first 2 values are
taken to be the slope and intercept.
Graphical parameters can be specified as arguments to
abline, see par for details.