Preliminary Computations to Add Linear Regression Line

USAGE:

prepanel.lmline(x, y) 

ARGUMENTS:

x
a vector of predictor values.
y
a vector of response values.

VALUE:

a list with components
dx
the change in x of the fitted line. Together with dy, this line is used in banking computations to determine the aspect ratio of the Trellis plot.
dy
the change in y of the line fitted line.
xlim
a vector of length 2 giving the minimum and maximum values for the x coordinates on the plot, taking into account the original data as well as the fitted line.
ylim
similar to xlim, but dealing with the y coordinates of the original data and the fit.