Variogram.corSpher           package:nlme           R Documentation

Calculate Semi-variogram for a corSpher Object

Description:

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

Usage:

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

Arguments:

  object: an object inheriting from class 'corSpher', representing an
          Spherical 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'.

     ...: 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:

     'corSpher', 'plot.Variogram', 'Variogram'

Examples:

     cs1 <- corSpher(15, form = ~ Time | Rat)
     cs1 <- Initialize(cs1, BodyWeight)
     Variogram(cs1)[1:10,]

