Variogram.corSpatial          package:nlme          R Documentation

Calculate Semi-variogram for a corSpatial Object

Description:

     This method function calculates the semi-variogram values
     corresponding to the model defined in 'FUN', using the estimated
     coefficients corresponding to 'object', at the distances defined
     by 'distance'.

Usage:

     ## S3 method for class 'corSpatial':
     Variogram(object, distance, sig2, length.out, FUN, ...)

Arguments:

  object: an object inheriting from class 'corSpatial', representing
          spatial correlation structure.

distance: an optional numeric vector with the distances at which the
          semi-variogram is to be calculated. Defaults to 'NULL', in
          which case a sequence of length 'length.out' between the
          minimum and maximum values of 'getCovariate(object)' is used.

    sig2: an optional numeric value representing the process variance.
          Defaults to '1'.

length.out: an optional integer specifying the length of the sequence
          of distances to be used for calculating the semi-variogram,
          when 'distance = NULL'. Defaults to '50'.

     FUN: a function of two arguments, the distance and the range
          corresponding to 'object', specifying the semi-variogram
          model.

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

Value:

     a data frame with columns 'variog' and 'dist' representing,
     respectively, the semi-variogram values and the corresponding
     distances. The returned value inherits from class 'Variogram'.

Author(s):

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

References:

     Cressie, N.A.C. (1993), "Statistics for Spatial Data", J. Wiley &
     Sons.

See Also:

     'corSpatial', 'Variogram', 'Variogram.default',
     'Variogram.corExp', 'Variogram.corGaus', 'Variogram.corLin',
     'Variogram.corRatio', 'Variogram.corSpher', 'plot.Variogram'

Examples:

     cs1 <- corExp(3, form = ~ Time | Rat)
     cs1 <- Initialize(cs1, BodyWeight)
     Variogram(cs1, FUN = function(x, y) (1 - exp(-x/y)))[1:10,]

