R: Outline an approximate pairwise confidence region
ellipse.nls
R Documentation
Outline an approximate pairwise confidence region
Description
This function produces the ellipsoidal outline of an approximate
pairwise confidence region for a nonlinear model fit.
Usage
## S3 method for class 'nls'
ellipse(x, which = c(1, 2), level = 0.95,
t = sqrt(2 * qf(level, 2, s$df[2])), ...)
Arguments
x
The first argument should be an nls object, usually resulting from a call
to nls().
which
Which selects the pair of parameters to be plotted. The default is the
first two.
level
The confidence level of the region. Default 95%.
t
The t statistic on the boundary of the ellipse.
...
Other ellipse.default parameters may also be used.
Details
The summary function is used to obtain the approximate covariance matrix of the
fitted parameters.
Value
A matrix with columns x and y to outline the confidence region.
See Also
ellipse.default, ellipse.profile
Examples
# Plot an approximate 95% confidence region for the weight and displacement
# parameters in the Michaelis Menten model
data(Puromycin)
fit <- nls(rate ~ Vm*conc/(K + conc), data = Puromycin, subset = state=="treated",
start = list(K = 0.05, Vm = 200))
plot(ellipse(fit,which=c('Vm','K')), type = 'l')
params <- fit$m$getPars()
points(params['Vm'],params['K'])