Defining smooths in GAM formulae
Function used in definition of smooth terms within
gam model formulae. The function does not evaluate a (spline)
smooth - it exist purely to help set up a model using spline based smooths.
- a list of variables that are the covariates that this smooth is a function of.
- the dimension of the basis used to represent the smooth term.
The default depends on the number of variables that the smooth is a
kshould not be less than the dimension of the null space of the penalty for the term (
- indicates whether the term is a fixed d.f. regression
TRUE) or a penalized regression spline (
- this can be
"cr"for a cubic regression spline or
"tp"for a thin plate regression spline. Only thin plate regression splines can be used for multidimensional smooths, so this argument only has an effect for univariat
- The order of the penalty for this t.p.r.s. term (e.g. 2 for normal cubic spline penalty with 2nd derivatives). O signals autoinitialization, which sets the order to the lowest value satisfying 2m>d+1, where d is the number of covariates: this
The function does not evaluate the variable arguments. It will
correctly interpret calls like
s(x,14|f) (results in pure
regression spline smooth of one variable with a 14 knot cubic
regression spline basis),
s(x,z,20) (a penalized regression
spline of 2 covariates using a 20 dimensional t.p.r.s. basis),
etc. but this feature is purely for back compatibility reasons, and
may not be maintained indefinitely.
- A list with the following items:
term An array of text strings giving the names of the covariates that the term is a function of. bs.dim The dimension of the basis used to represent the smooth. bs.type The type of basis. 0 is cubic regression spline. 1 is thin plate regression spline. 0 can only be used for 1-d smooths. fixed TRUE if the term is to be treated as a pure regression spline (with fixed degrees of freedom); FALSE if it is to be treated as a penalized regression spline dim The dimension of the smoother - i.e. the number of covariates that it is a function of. p.order The order of the t.p.r.s. penalty, or 0 for auto-selection of the penalty order. full.call Text for pasting into a string to be converted to a gam formula, which has the values of function options given explicitly - this is useful for constructing a fully expanded gam formula which can be used without needing access to any variables that may have been used to define k, fx, bs or m in the original call. i.e. this is text which when parsed and evaluated generates a call to
s()with all the options spelled out explicitly.