Add Linear Regression Line to Panel

USAGE:

panel.lmline(x, y, ...) 

ARGUMENTS:

x
a vector of predictor values.
y
a vector of response values.
...
graphical parameters may be passed to this function.

SIDE EFFECTS:

A regression line, from fitting y = a*x + b is drawn on the plot.

EXAMPLES:

# The function is simple: 
panel.lmline <- function(x, y, ...) 
        panel.abline(lm(y ~ x), ...)