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crs: Bases for cubic regression splines (equivalent to "cr" in mgcv)

Description

Builds the design matrix and the penalty matrix for cubic regression splines.

Usage

crs(x, knots = NULL, df = 10, intercept = TRUE)

Value

List of three elements

bs

design matrix

pen

penalty matrix

knots

vector of knots (specified or calculated from df)

Arguments

x

Numeric vector

knots

Numeric vectors that specifies the knots of the splines (including boundaries); default is NULL

df

numeric value that indicates the number of knots desired (or degrees of freedom) if knots=NULL; default is 10

intercept

if FALSE, the intercept is excluded from the basis; default is TRUE

Details

See package mgcv and section 4.1.2 of Wood (2006) for more details about this basis

References

Wood, S. N. (2006), Generalized additive models: an introduction with R. London: Chapman & Hall/CRC.

Examples

Run this code
x <- seq(1,10,length=100)
# natural cubic spline with 3 knots
crs(x,knots=c(1,5,10))

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