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, ...)
Arguments
object | an object inheriting from class |
distance | an optional numeric vector with the distances between residual pairs. If a grouping variable is present, only the distances between residual pairs within the same group should be given. If missing, the distances are calculated based on the values of the arguments |
form | an optional one-sided formula specifying the covariate(s) to be used for calculating the distances between residual pairs and, optionally, a grouping factor for partitioning the residuals (which must appear to the right of a |
resType | an optional character string specifying the type of residuals to be used. If |
data | an optional data frame in which to interpret the variables in |
na.action | a function that indicates what should happen when the data contain |
maxDist | an optional numeric value for the maximum distance used for calculating the semi-variogram between two residuals. By default all residual pairs are included. |
length.out | an optional integer value. When |
collapse | an optional character string specifying the type of collapsing to be applied to the individual semi-variogram values. If equal to |
nint | an optional integer with the number of intervals to be used when collapsing the semi-variogram values. Defaults to |
robust | an optional logical value specifying if a robust semi-variogram estimator should be used when collapsing the individual values. If |
breaks | an optional numeric vector with the breakpoints for the distance intervals to be used in collapsing the semi-variogram values. If not missing, the option specified in |
metric | an optional character string specifying the distance metric to be used. The currently available options are |
... | 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. 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
.
Author(s)
José Pinheiro and Douglas Bates [email protected]
References
Cressie, N.A.C. (1993), "Statistics for Spatial Data", J. Wiley & Sons.
See Also
gls
, Variogram
, Variogram.default
, Variogram.lme
, plot.Variogram
Examples
fm1 <- gls(weight ~ Time * Diet, BodyWeight) Vm1 <- Variogram(fm1, form = ~ Time | Rat) print(head(Vm1), digits = 3)
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Licensed under the GNU General Public License.