plot.profile: Plotting Functions for 'profile' Objects

Description

plot and pairs methods for objects of class "profile".

Usage

# S3 method for profile
plot(x, ...)
# S3 method for profile
pairs(x, colours = 2:3, ...)

Arguments

x: an object inheriting from class "profile".
colours: Colours to be used for the mean curves conditional on x and y respectively.
...: arguments passed to or from other methods.

Author

Originally, D. M. Bates and W. N. Venables. (For S in 1996.)

Details

This is the main plot method for objects created by profile.glm. It can also be called on objects created by profile.nls, but they have a specific method, plot.profile.nls.

The pairs method shows, for each pair of parameters x and y, two curves intersecting at the maximum likelihood estimate, which give the loci of the points at which the tangents to the contours of the bivariate profile likelihood become vertical and horizontal, respectively. In the case of an exactly bivariate normal profile likelihood, these two curves would be straight lines giving the conditional means of y|x and x|y, and the contours would be exactly elliptical.

Examples

Run this code

## see ?profile.glm for an example using glm fits.

## a version of example(profile.nls) from R >= 2.8.0
fm1 <- nls(demand ~ SSasympOrig(Time, A, lrc), data = BOD)
pr1 <- profile(fm1, alpha = 0.1)
MASS:::plot.profile(pr1)
pairs(pr1) # a little odd since the parameters are highly correlated

## an example from ?nls
x <- -(1:100)/10
y <- 100 + 10 * exp(x / 2) + rnorm(x)/10
nlmod <- nls(y ~  Const + A * exp(B * x), start=list(Const=100, A=10, B=1))
pairs(profile(nlmod))