R: An Internal Function for Extracting (Some) Formation and...

.extract.fd.formulae {tergm} | R Documentation

## An Internal Function for Extracting (Some) Formation and Dissolution Formulas from a Combined Formula

### Description

This function is used in `tergm.EGMME.initialfit` and also when targets or monitoring formulas are specified by characters. It makes a basic attempt to identify the formation and dissolution formulas within a larger combined formula (which may also include non-separable terms). Instances of `Form` at the top level (which may occur inside `offset`) contribute to the formation formula; instances of `Persist` and `Diss` at the top level (which may also occur inside `offset`) contribute to the dissolution formula. All other terms are regarded as non-separable; this includes instances of `Form`, `Persist`, and `Diss` that occur inside other operator terms, including inside `Offset`, and also includes all interactions at the top level (for which the top level term is effectively the interaction operator `*` or `:`), whether or not they include `Form`, `Persist`, and/or `Diss`. The formation and dissolution formulas are obtained by adding the contributing terms, replacing `Form` and `Persist` with trivial operators that protect the environments of their formula arguments but have no effect on statistics or coefficient names (meaning the formulas effectively become cross-sectional), and replacing `Diss` by a similar operator that negates statistics. These are included in the return value as the `form` and `pers` elements of the list (the "dissolution" formula really being the persistence formula), which also includes the formula of non-separable terms as `nonsep`, and the formula of all terms after replacing `Form`, `Persist`, and `Diss` as described above as `all`.

If usage proves problematic, one may specify the monitoring and/or targets formulas explicitly (rather than by characters), and one may pass initial coefficient values for the EGMME to avoid running `tergm.EGMME.initialfit`.

### Usage

    .extract.fd.formulae(formula)

### Arguments

`formula` | a `formula`.

### Value

A `list` containing `form`, `pers`, `nonsep`, and `all` formulas as described above.

[Package tergm version 4.0.2 Index]