# corGrafen

##### Grafen's (1989) Correlation Structure

Grafen's (1989) covariance structure. Branch lengths are computed using
Grafen's method (see `compute.brlen`

). The covariance
matrice is then the traditional variance-covariance matrix for a
phylogeny.

- Keywords
- models

##### Usage

```
corGrafen(value, phy, form=~1, fixed = FALSE)
# S3 method for corGrafen
coef(object, unconstrained = TRUE, ...)
# S3 method for corGrafen
corMatrix(object,
covariate = getCovariate(object), corr = TRUE, ...)
```

##### Arguments

- value
The \(\rho\) parameter

- phy
An object of class

`phylo`

representing the phylogeny (branch lengths are ignored) to consider- object
An (initialized) object of class

`corGrafen`

- corr
a logical value. If 'TRUE' the function returns the correlation matrix, otherwise it returns the variance/covariance matrix.

- fixed
an optional logical value indicating whether the coefficients should be allowed to vary in the optimization, or kept fixed at their initial value. Defaults to 'FALSE', in which case the coefficients are allowed to vary.

- form
ignored for now.

- covariate
ignored for now.

- unconstrained
a logical value. If 'TRUE' the coefficients are returned in unconstrained form (the same used in the optimization algorithm). If 'FALSE' the coefficients are returned in "natural", possibly constrained, form. Defaults to 'TRUE'

- …
some methods for these generics require additional arguments. None are used in these methods.

##### Value

An object of class `corGrafen`

or the rho coefficient from an
object of this class or the correlation matrix of an initialized
object of this class.

##### References

Grafen, A. (1989) The phylogenetic regression. *Philosophical
Transactions of the Royal society of London. Series B. Biological
Sciences*, **326**, 119--157.

##### See Also

*Documentation reproduced from package ape, version 5.3, License: GPL (>= 2)*