Variogram.lme: Calculate Semi-variogram for Residuals from an lme Object
Description
This method function calculates the semi-variogram for the
within-group residuals from an lme fit. The semi-variogram
values are calculated for pairs of residuals within the same group. If
collapse is different from "none", the individual
semi-variogram values are collapsed using either a robust estimator
(robust = TRUE) defined in Cressie (1993), or the average of
the values within the same distance interval. The semi-variogram is
useful for modeling the error term correlation structure.
Usage
## S3 method for class 'lme':
Variogram(object, distance, form, resType, data,
na.action, maxDist, length.out, collapse, nint, breaks,
robust, metric, \dots)
Arguments
Value
a data frame with columns variog and dist representing,
respectively, the semi-variogram values and the corresponding
distances. If the semi-variogram values are collapsed, an extra
column, n.pairs, with the number of residual pairs used in each
semi-variogram calculation, is included in the returned data frame. If
object includes a corSpatial element, a data frame with
its corresponding semi-variogram is included in the returned value, as
an attribute "modelVariog". The returned value inherits from
class Variogram.
References
Cressie, N.A.C. (1993), "Statistics for Spatial Data", J. Wiley & Sons.