# Inv: Specify the Reciprocal of a Predictor in a gnm Model Formula In gnm: Generalized Nonlinear Models

 Inv 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

`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)
```

gnm documentation built on April 29, 2022, 5:06 p.m.