fd2coef | R Documentation |
This function computes the coefficients of functional data in a B-spline basis.
fd2coef(x, basis, byrow = TRUE)
x |
matrix of functional data. |
basis |
object created by |
.
byrow |
are the functional data stored in rows (TRUE) or in columns (FALSE)? |
A matrix of B-spline coefficients stored in the same format (row or columns) as functional data.
In view of (online or offline) functional PCA,
the coefficients are smoothed and premultiplied by M^{1/2}
,
with M
the Gram matrix associated to the B-spline matrix.
create.basis
, coef2fd
n <- 100 # number of curves
d <- 500 # number of observation points
grid <- (1:d)/d # observation points
p <- 50 # number of B-spline basis functions
# Simulate Brownian motion
x <- matrix(rnorm(n*d,sd=1/sqrt(d)),n,d)
x <- t(apply(x,1,cumsum))
# Create B-spline basis
mybasis <- create.basis(grid, p, 1e-4)
# Compute smooth basis coefficients
beta <- fd2coef(x, mybasis)
# Recover smooth functional data
x.smooth <- coef2fd(beta, mybasis)
# Standard PCA and Functional PCA
pca <- prcomp(x)
fpca <- prcomp(beta)
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