Extends formula's with predictor matrix settings

```
extend.formulas(formulas, data, blocks, predictorMatrix = NULL,
auxiliary = TRUE, include.intercept = FALSE, ...)
```

formulas

A named list of formula's, or expressions that
can be converted into formula's by `as.formula`

. List elements
correspond to blocks. The block to which the list element applies is
identified by its name, so list names must correspond to block names.
The `formulas`

argument is an alternative to the
`predictorMatrix`

argument that allows for more flexibility in
specifying imputation models, e.g., for specifying interaction terms.

data

A data frame or a matrix containing the incomplete data. Missing
values are coded as `NA`

.

blocks

List of vectors with variable names per block. List elements
may be named to identify blocks. Variables within a block are
imputed by a multivariate imputation method
(see `method`

argument). By default each variable is placed
into its own block, which is effectively
fully conditional specification (FCS) by univariate models
(variable-by-variable imputation). Only variables whose names appear in
`blocks`

are imputed. The relevant columns in the `where`

matrix are set to `FALSE`

of variables that are not block members.
A variable may appear in multiple blocks. In that case, it is
effectively re-imputed each time that it is visited.

predictorMatrix

A numeric matrix of `length(blocks)`

rows
and `ncol(data)`

columns, containing 0/1 data specifying
the set of predictors to be used for each target column.
Each row corresponds to a variable block, i.e., a set of variables
to be imputed. A value of `1`

means that the column
variable is used as a predictor for the target block (in the rows).
By default, the `predictorMatrix`

is a square matrix of `ncol(data)`

rows and columns with all 1's, except for the diagonal.
Note: For two-level imputation models (which have `"2l"`

in their names)
other codes (e.g, `2`

or `-2`

) are also allowed.

auxiliary

A logical that indicates whether the variables
listed in `predictors`

should be added to the formula as main
effects. The default is `TRUE`

.

include.intercept

A logical that indicated whether the intercept should be included in the result.

...

Named arguments that are passed down to the univariate imputation functions.

A list of formula's