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

Exp {gnm} | R Documentation

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

### Description

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

### Usage

    Exp(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 `Exp`
`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 and David Firth

### See Also

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

### Examples

    set.seed(1)

    ## Using 'Mult' with 'Exp' to constrain the first constituent multiplier
    ##  to be non-negative

    ## Fit the "UNIDIFF" mobility model across education levels
    unidiff <- gnm(Freq ~ educ*orig + educ*dest +
                   Mult(Exp(educ), orig:dest),
                   family = poisson, data = yaish, subset = (dest != 7))

[Package gnm version 1.1-2 Index]