R: Convert a curved ERGM into a form suitable as initial values...

enformulate.curved {ergm} | R Documentation

## Convert a curved ERGM into a form suitable as initial values for the same ergm.

### Description

The generic `enformulate.curved` converts an `ergm` object or formula of a model with curved terms to the variant in which the curved parameters embedded into the formula and are removed from the parameter vector. This is the form required by `ergm` calls.

### Usage

    ## S3 method for class 'ergm'
    enformulate.curved(object, ...)
    ## S3 method for class 'formula'
    enformulate.curved(object, theta, response=NULL, ...)

### Arguments

`object` | An `ergm` object or an ERGM formula. The curved terms of the given formula (or the formula used in the fit) must have all of their arguments passed by name.
`theta` | Curved model parameter configuration.
`response` | Not for release.
`...` | Unused at this time.

### Details

Because of a current kludge in `ergm`, output from one run cannot be directly passed as initial values (`control.ergm(init=)`) for the next run if any of the terms are curved. One workaround is to embed the curved parameters into the formula (while keeping `fixed=FALSE`) and remove them from `control.ergm(init=)`.

This function automates this process for curved ERGM terms included with the `ergm` package. It does not work with curved terms not included in ergm.

### Value

A list with the following components:

`formula` | The formula with curved parameter estimates incorporated.
`theta` | The coefficient vector with curved parameter estimates removed.

### See Also

`ergm`, `simulate.ergm`

### Examples

    data(sampson)
    gest<-ergm(samplike~edges+gwesp(decay=.5, fixed=FALSE),
        control=control.ergm(MCMLE.maxit=1))
    # Error:
    gest2<-try(ergm(gest$formula, control=control.ergm(init=coef(gest), MCMLE.maxit=2)))
    print(gest2)

    # Works:
    tmp<-enformulate.curved(gest)
    tmp
    gest2<-try(ergm(tmp$formula, control=control.ergm(init=tmp$theta, MCMLE.maxit=2)))
    summary(gest2)

[Package ergm version 3.8.0 Index]