# s

From mgcv v0.6-1
by Simon Wood

##### 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.

- Keywords
- models, regression, smooth

##### Usage

`s(..., k=-1,fx=FALSE,bs="tp",m=0)`

##### Arguments

- ...
- a list of variables that are the covariates that this smooth is a function of.
- k
- the dimension of the basis used to represent the smooth term.
The default depends on the number of variables that the smooth is a
function of.
`k`

should not be less than the dimension of the null space of the penalty for the term ( - fx
- indicates whether the term is a fixed d.f. regression
spline (
`TRUE`

) or a penalized regression spline (`FALSE`

). - bs
- 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 - m
- 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

##### Details

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.

##### Value

- 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.

##### See Also

*Documentation reproduced from package mgcv, version 0.6-1, License: GPL version 2 or later*

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