# pdMatrix {nlme}

### Description

The positive-definite matrix represented by `object`

, or a square-root factor of it is obtained. Letting S denote a positive-definite matrix, a square-root factor of S is any square matrix L such that . This function extracts S or L.

### Usage

pdMatrix(object, factor)

### Arguments

- object
- an object inheriting from class
`pdMat`

, representing a positive definite matrix. - factor
- an optional logical value. If
`TRUE`

, a square-root factor of the positive-definite matrix represented by`object`

is returned; else, if`FALSE`

, the positive-definite matrix is returned. Defaults to`FALSE`

.

### Values

if `fact`

is `FALSE`

the positive-definite matrix represented by `object`

is returned; else a square-root of the positive-definite matrix is returned.

### References

Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S and S-PLUS", Springer, esp. p. 162.

Documentation reproduced from package nlme, version 3.1-124. License: GPL (>= 2)