R: Specify the Reciprocal of a Predictor in a gnm Model Formula

Inv {gnm} | R Documentation

## Specify the Reciprocal of a Predictor in a gnm Model Formula

### Description

A function of class `"nonlin"` to specify the reciprocal of a predictor in the formula argument to `gnm`.

### Usage

    Inv(expression, inst = NULL)

### Arguments

`expression` | a symbolic expression representing the (possibly nonlinear) predictor.
`inst` | (optional) an integer specifying the instance number of the term.

### Details

The `expression` argument is interpreted as the right hand side of a formula in an object of class `"formula"`, except that an intercept term is not added by default. Any function of class `"nonlin"` may be used in addition to the usual operators and functions.

### Value

A list with the components required of a `"nonlin"` function:

`predictors` | the `expression` argument passed to `Inv`
`term` | a function to create a deparsed mathematical expression of the term, given a label for the predictor.
`call` | the call to use as a prefix for parameter labels.

### Author(s)

Heather Turner

### See Also

`gnm`, `formula`, `nonlin.function`

### Examples

    ## One way to fit the logistic function without conditional
    ## linearity as in ?nls
    library(gnm)
    set.seed(1)
    DNase1 <- subset(DNase, Run == 1)

    test <- gnm(density ~ -1 +
                Mult(1, Inv(Const(1) + Exp(Mult(1 + offset(-log(conc)),
                                                    Inv(1))))),
                start = c(NA, 0, 1), data = DNase1, trace = TRUE)
    coef(test)

[Package gnm version 1.1-2 Index]