Variogram.default            package:nlme            R Documentation

Calculate Semi-variogram

Description:

     This method function calculates the semi-variogram for an
     arbitrary vector 'object', according to the distances in
     'distance'. For each pair of elements x,y in 'object', the
     corresponding semi-variogram is (x-y)^2/2. The semi-variogram is
     useful for identifying and modeling spatial correlation structures
     in observations with constant expectation and constant variance.

Usage:

     ## Default S3 method:
     Variogram(object, distance, ...)

Arguments:

  object: a numeric vector with the values to be used for calculating
          the semi-variogram, usually a residual vector from a fitted
          model.

distance: a numeric vector with the pairwise distances corresponding to
          the elements of 'object'. The order of the elements in
          'distance' must correspond to the pairs '(1,2), (1,3), ...,
          (n-1,n)', with 'n' representing the length of 'object', and
          must have length 'n(n-1)/2'.

     ...: 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:

     'Variogram.gls', 'Variogram.lme', 'plot.Variogram'

Examples:

     data(Ovary)
     ## Not run: 
     fm1 <- lm(follicles ~ sin(2 * pi * Time) + cos(2 * pi * Time), Ovary,
               subset = Mare == 1)
     Variogram(resid(fm1), dist(1:29))[1:10,]
     ## End(Not run)

