pdMatrix                package:nlme                R Documentation

Extract Matrix or Square-Root Factor from a pdMat Object

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 S = L'L. 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'.

Value:

     if 'fact' is 'FALSE' the positive-definite matrix represented by
     'object' is returned; else a square-root of the positive-definite
     matrix is returned.

Author(s):

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

References:

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

See Also:

     'as.matrix.pdMat', 'pdClasses', 'pdFactor', 'pdMat',
     'pdMatrix.reStruct', 'corMatrix'

Examples:

     pd1 <- pdSymm(diag(1:4))
     pdMatrix(pd1)

