R: Outline an approximate pairwise confidence region

ellipse.nls {ellipse} | 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'])

[Package ellipse version 0.3-8 Index]