knot.select: knot.selector: produce knot vector for splineDesign

In floswald/gridR: gridR: create different scalings of uniformly spaced grids.

Description

select knots for splineDesign at quantiles of data or at user-specified locations.

Usage

  knot.select(degree, x, num.basis = NULL, plotit = FALSE)

Arguments

degree	positive integer for spline degree
x	numeric vector of data sites or desired spline knots
num.basis	optional.
plotit	logical of whether plot result

Details

user selects degree of spline and optionally the number of desired basis functions. If num.basis is not NULL, function produces a knot vector on supplied data vector x, where the remaining interior knots are placed at the quantiles of x. Remaining means "after beginning/end multiplicity was constructed". If num.basis is NULL, the interior knots are given by x[-c(1,length(x))] (i.e. all but first and last element of x) and num.basis is chosen accordingly. The relationship is num.basis = length(knots) - degree - 1. The minimum number of basis functions to obtain a valid knot vector with correct multiplicity is min(num.basis) = deg + 1. The function overrides choices where num.basis is too small with a warning.

Value

numeric vector of spline knots of length num.basis + degree + 1, with knot multiplicity degree+1 of class knotVec with attribute num.basis.

References

http://www.cs.mtu.edu/~shene/COURSES/cs3621/NOTES/spline/B-spline/bspline-basis.html, http://www.uio.no/studier/emner/matnat/ifi/INF-MAT5340/v07/undervisningsmateriale/

Examples

knot.select(degree=4,x=1:10)
knot.select(degree=3,x=1:10,num.basis=8,plotit=TRUE)
knot.select(degree=3,x=1:10,num.basis=3)  # warning
knot.select(degree=1,x=1:10,num.basis=2)
knot.select(degree=4,x=1:10)
knot.select(degree=3,x=1:10,num.basis=6,plotit=TRUE)
#
# make a double exponentially-scaled grid and use as knots
#
log.grid <- grid.maker(c(-10,15),20,spacing="log.g2")
knot.select(degree=4,x=log.grid,num.basis=NULL,TRUE)
#
# choose number of basis funs on same grid: remaining interior (after constructing multiplicities)
# knots will be placed at quantiles of grid
#
knot.select(degree=4,x=log.grid,num.basis=8,TRUE)
#
# make a hyperbolic-sine-scaled grid and use as knots
#
hyp.grid <- grid.maker(c(-10,15),20,spacing="hyp.sine")
knot.select(degree=5,x=hyp.grid,num.basis=NULL,TRUE)
#
# choose number of basis funs on same grid
#
knot.select(degree=5,x=hyp.grid,num.basis=9,TRUE)

floswald/gridR documentation built on May 16, 2019, 1:24 p.m.