value
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an optional vector with the parameter values in
constrained form. If nugget is FALSE , value can
have only one element, corresponding to the "range" of the spatial
correlation structure, which must be greater than zero. If
nugget is TRUE , meaning that a nugget effect is
present, value can contain one or two elements, the first
being the "range" and the second the "nugget ratio" (the ratio
between the variance of an observation and the covariance between two
observations taken arbitrarily close together); the first must be
greater than zero and the second must be between zero and
one. Defaults to numeric(0) , which results in a range of 90%
of the minimum distance and a nugget ratio of 0.9 being assigned to
the parameters when object is initialized.
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form
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a one sided formula of the form ~ S1+...+Sp , or
~ S1+...+Sp | g , specifying spatial covariates S1
through Sp and, optionally, a grouping factor g .
When a grouping factor is present in form , the correlation
structure is assumed to apply only to observations within the same
grouping level; observations with different grouping levels are
assumed to be uncorrelated. Defaults to ~ 1 , which corresponds
to using the order of the observations in the data as a covariate,
and no groups.
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nugget
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an optional logical value indicating whether a nugget
effect is present. Defaults to FALSE .
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type
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an optional character string specifying the desired type of
correlation structure. Available types include "spherical" ,
"exponential" , "gaussian" , and "linear" . See the
documentation on the functions corSpher , corExp ,
corGaus , and corLin for a description of these
correlation structures. Partial matching of arguments is used, so
only the first character needs to be provided.Defaults to
"spherical" .
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metric
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an optional character string specifying the distance
metric to be used. The currently available options are
"euclidian" for the root sum-of-squares of distances;
"maximum" for the maximum difference; and "manhattan"
for the sum of the absolute differences. Partial matching of
arguments is used, so only the first three characters need to be
provided.Defaults to "euclidian" .
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