cpar: Conditionally parametric term for a Locfit model.
Description
A term entered in a locfit model formula using
cpar will result in a fit that is conditionally parametric.
If the formula is y~x1+cpar(x2), the resulting surface,
for fixed x1, will be quadratic (using the default deg=2)
in x2. Note that the coefficients of the quadratic may depend
on x1; this distinguishes a conditionally parametric model
from a semiparametric model.
data(ethanol)
# fit a conditionally parametric modelfit <- locfit(NOx~E+cpar(C),data=ethanol)
plot(fit)
# one way to force a parametric fit with locfitfit <- locfit(NOx~cpar(E),data=ethanol)