Plotting Guide
The links below will take you to the corresponding R files. They contain very useful information.
Did you know there are nine different ways to calculate quantiles in R? The default method is not even the recommended method!
Please take a look at them if you get hung up on something.
Fitting is done locally. That is, for the fit at point x, the fit is made using points in a neighborhood of x, weighted by their distance from x (with differences in 'parametric' variables being ignored when computing the distance). The size of the neighborhood is controlled by 'alpha' (set by span or enp.target). For 'alpha'< 1, the neighbourhood includes proportion 'alpha' of the points, and these have tricubic weighting (proportional to (1 - (dist/maxdist)^3)^3. For 'alpha' > 1, all points are used, with the 'maximum distance' assumed to be 'alpha'^1/p times the actual maximum distance for 'p' explanatory variables.
For the default family, fitting is by (weighted) least squares. For family="symmetric" a few iterations of an M-estimation procedure with Tukey's biweight are used. Be aware that as the initial value is the least-squares fit, this need not be a very resistant fit.
add.line <- trellis.par.get("add.line")
add.line$col <- "red"
trellis.par.set("add.line", add.line)
Text from the 'par' document from the graphics package. It is valid for any function dealing with lines.