Variogram.default {nlme}

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)

José Pinheiro and Douglas Bates [e-mail]

References

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

See Also

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

Examples

fm1 <- lm(follicles ~ sin(2 * pi * Time) + cos(2 * pi * Time), Ovary,
          subset = Mare == 1)
Variogram(resid(fm1), dist(1:29))[1:10,]