preplot.locfit can be called directly, although it is more usual
to call plot.locfit or predict.locfit.
The advantage of preplot.locfit is in S-Plus 5, where arithmetic
and transformations can be performed on the "preplot.locfit"
object. plot(preplot(fit)) is essentially synonymous with plot(fit).
## S3 method for class 'locfit':
preplot(object, newdata=NULL, where, tr=NULL, what="coef",
band="none", get.data=FALSE, f3d=FALSE, \dots)locfit().newdata. Choices include
"grid" for the grid lfmarg(object);
"data" for the original data points and "fitp" for the
direct fiwhat="coef", works with the fitted curve itself. Other
choices include "nlx" for the length of the weight diagram;
"infl" for the influence function; "none". Other
choices include "global" for bands using a global variance
estimate; "local" for bands usiTRUE, the original data is attached to the
returned object, and added to the plot.TRUE, sets a flag that forces ploting using the
trellis style. Not available in R."preplot.locfit", containing the predicted
values and additional information used to construct the plot.locfit, predict.locfit, plot.locfit.