approx.Z {lmeSplines} | R Documentation |
Function to interpolate the Z-matrix for LME smoothing spline fits
from one set of values of the time
covariate to another.
approx.Z(Z, oldtimes, newtimes)
Z |
Z-matrix with rows corresponding to the sorted unique
values of the time covariate |
oldtimes |
original (sorted) values for time covariate,
corresponding to the rows of Z |
newtimes |
new (sorted) values for time covariate |
Uses linear interpolation of each column of the Z-matrix, regarded as
a function of time, with the times given by oldtimes
.
A matrix corresponding to an interpolated spline matrix. Can be used
with smspline()
for fitting LME splines with random effects
corresponding to a different set of values of the time
covariate
than those represented in the data, or as part of the `newdata' argument
prediction from an existing model, to obtain predictions at points
not represented in the data using predict.lme()
.
Linear interpolation works well here because the spline basis functions are approximately piecewise linear.
Rod Ball rod.ball@forestresearch.co.nz www.forestresearch.co.nz
times1 <- 1:10 Zt1 <- smspline(~ times1) times2 <- seq(1,10,by=0.1) Zt2 <- approx.Z(Zt1,oldtimes=times1,newtimes=times2)