Outline an approximate pairwise confidence region — ellipse.nls • ellipse

This function produces the ellipsoidal outline of an approximate pairwise confidence region for a nonlinear model fit.

Usage

# S3 method for nls
ellipse(x, which = c(1, 2), level = 0.95, 
    t = sqrt(2 * qf(level, 2, s$df[2])), ...)

Arguments

x: The first argument should be an nls object, usually resulting from a call to nls().
which: Which selects the pair of parameters to be plotted. The default is the first two.
level: The confidence level of the region. Default 95%.
t: The t statistic on the boundary of the ellipse.
...: Other ellipse.default parameters may also be used.

Value

A matrix with columns x and y to outline the confidence region.

Details

The summary function is used to obtain the approximate covariance matrix of the fitted parameters.

See also

ellipse.default, ellipse.profile

Examples

# Plot an approximate 95% confidence region for the weight and displacement
# parameters in the Michaelis Menten model
data(Puromycin)
fit <- nls(rate ~ Vm*conc/(K + conc), data = Puromycin, subset = state=="treated", 
    start = list(K = 0.05, Vm = 200))
plot(ellipse(fit,which=c('Vm','K')), type = 'l')
params <- fit$m$getPars()
points(params['Vm'],params['K'])