Variogram.gls: Calculate Semi-variogram for Residuals from a gls Object
Description
This method function calculates the semi-variogram for the residuals
from a gls fit. The semi-variogram values are calculated for
pairs of residuals within the same group level, if a grouping factor
is present. 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 'gls':
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.