nlsModel {stats}R Documentation

Create an nlsModel Object

Description

This is the constructor for nlsModel objects, which are function closures for several functions in a list. The closure includes a nonlinear model formula, data values for the formula, as well as parameters and their values.

Usage

nlsModel(form, data, start)

Arguments

form a nonlinear model formula
data a data frame or a list in which to evaluate the variables from the model formula
start a named list or named numeric vector of starting estimates for the parameters in the model

Details

An nlsModel object is primarily used within the nls function. It encapsulates the model, the data, and the parameters in an environment and provides several methods to access characteristics of the model. It forms an important component of the object returned by the nls function.

See nls for where elements of the formula form are looked for. In normal use all the variables will be in data.

Value

The value is a list of functions that share a common environment.

resid returns the residual vector evaluated at the current parameter values
fitted returns the fitted responses and their gradient at the current parameter values
formula returns the model formula
deviance returns the residual sum-of-squares at the current parameter values
gradient returns the gradient of the model function at the current parameter values
conv returns the relative-offset convergence criterion evaluated at the current parmeter values
incr returns the parameter increment calculated according to the Gauss-Newton formula
setPars a function with one argument, pars. It sets the parameter values for the nlsModel object and returns a logical value denoting a singular gradient array.
getPars returns the current value of the model parameters as a numeric vector
getAllPars returns the current value of the model parameters as a numeric vector
getEnv returns the environment shared by these functions, which contains copies of all the variables in data and has as parent the environment of form.
trace the function that is called at each iteration if tracing is enabled
Rmat the upper triangular factor of the gradient array at the current parameter values
predict takes as argument newdata,a data.frame and returns the predicted response for newdata.

Author(s)

Douglas M. Bates and Saikat DebRoy

References

Bates, D.M. and Watts, D.G. (1988), Nonlinear Regression Analysis and Its Applications, Wiley

See Also

nls

Examples

DNase1 <- DNase[ DNase$Run == 1, ]
mod <-
 nlsModel(density ~ SSlogis( log(conc), Asym, xmid, scal ),
          DNase1, list( Asym = 3, xmid = 0, scal = 1 ))
mod$getPars()     # returns the parameters as a list
mod$deviance()    # returns the residual sum-of-squares
mod$resid()       # returns the residual vector and the gradient
mod$incr()        # returns the suggested increment
mod$setPars( unlist(mod$getPars()) + mod$incr() )  # set new parameter values
mod$getPars()     # check the parameters have changed
mod$deviance()    # see if the parameter increment was successful
mod$trace()       # check the tracing
mod$Rmat()        # R matrix from the QR decomposition of the gradient

[Package stats version 2.1.0 Index]