Matern.parameters.R
Matern.cor.to.range <- function(d, nu, cor.target = 0.5,
guess = NULL, ...) {
# define local function for root finding
#
ftemp <- function(theta, f.extra) {
Matern(f.extra$d/theta, nu = f.extra$nu) - f.extra$cor.target
}
# inital guess is exponential
if (is.null(guess)) {
guess[1] <- guess[2] <- -d/log(cor.target)
}
# extra info for function
f.extra = list(d = d, nu = nu, cor.target = cor.target)
# find guesses that are above and below
while (ftemp(guess[2], f.extra) < 0) {
guess[2] <- guess[2] * 2
}
while (ftemp(guess[1], f.extra) > 0) {
guess[1] <- guess[1]/2
}
temp <- bisection.search(guess[1], guess[2], f = ftemp, f.extra = f.extra,
...)
return(temp$x)
}