corFactor.corStruct {nlme} | R Documentation |

## Factor of a corStruct Object Matrix

### Description

This method function extracts a transpose inverse square-root factor,
or a series of transpose inverse square-root factors, of the
correlation matrix, or list of correlation matrices, represented by
`object`

. Letting *S* denote a correlation
matrix, a square-root factor of *S* is any square
matrix *L* such that *S = L'L*. This method
extracts *L^(-t)*.

### Usage

## S3 method for class 'corStruct':
corFactor(object, ...)

### Arguments

`object` |
an object inheriting from class `corStruct`
representing a correlation structure, which must have been
initialized (using `Initialize` ). |

`...` |
some methods for this generic require additional
arguments. None are used in this method. |

### Value

If the correlation structure does not include a grouping factor, the
returned value will be a vector with a transpose inverse square-root
factor of the correlation matrix associated with `object`

stacked
column-wise. If the correlation structure includes a grouping factor,
the returned value will be a vector with transpose inverse
square-root factors of the correlation matrices for each group, stacked
by group and stacked column-wise within each group.

### Note

This method function is used intensively in optimization
algorithms and its value is returned as a vector for efficiency
reasons. The `corMatrix`

method function can be used to obtain
transpose inverse square-root factors in matrix form.

### Author(s)

Jose Pinheiro Jose.Pinheiro@pharma.novartis.com and
Douglas Bates bates@stat.wisc.edu

### See Also

`corMatrix.corStruct`

,
`recalc.corStruct`

, `Initialize.corStruct`

### Examples

cs1 <- corAR1(form = ~1 | Subject)
cs1 <- Initialize(cs1, data = Orthodont)
corFactor(cs1)

[Package

*nlme* version 3.1-66

Index]