| lf {locfit} | R Documentation |
This function is used to specify a smooth term in a gam()
model formula.
At the time of writing, gam is not available in R.
lf(..., alpha=0.7, deg=2, scale=1, kern="tcub", ev="tree", maxk=100)
... |
numeric predictor variable(s) |
alpha |
Smoothing parameter. A single number (e.g. alpha=0.7)
is interpreted as a nearest neighbor fraction. With two
componentes (e.g. alpha=c(0.7,1.2)), the first component
is a nearest neighbor fraction, and the second component is
a fixed component. A third component is the penalty term in locally
adaptive smoothing. |
deg |
degree of polynomials to be fitted locally. |
scale |
A scale to apply to each variable. This is especially important for
multivariate fitting, where variables may be measured in
non-comparable units. It is also used to specify the frequency
for ang terms. If scale=FALSE (the default) no scaling
is performed. If scale=TRUE, marginal standard deviations are used.
Alternatively, a numeric vector can provide scales for the
individual variables. |
kern |
Weight function, default = "tcub".
Other choices are "rect", "trwt", "tria",
"epan", "bisq" and "gauss". Choices may be restricted
when derivatives are required; e.g. for confidence bands and some
bandwidth selectors. |
ev |
Evaluation Structure, default = "tree". Also available are
"phull", "data", "grid", "kdtree",
"kdcenter" and "crossval". ev="none" gives no
evaluation points, effectively producing the global parametric fit.
A vector or matrix of evaluation points can also be provided. |
maxk |
Controls space assignment for evaluation structures.
For the adaptive evaluation structures, it is impossible to be sure
in advance how many vertices will be generated. If you get
warnings about `Insufficient vertex space', Locfit's default assigment
can be increased by increasing maxk. The default is maxk=100. |
locfit,
locfit.raw,
gam.lf,
gam
# fit an additive semiparametric model to the ethanol data.
if (exists("gam")) { # shut up R's checks
fit <- gam(NOx~lf(E)+C,data=ethanol)
plot(fit)
}