corSpatial {nlme} | R Documentation |

This function is a constructor for the `corSpatial`

class,
representing a spatial correlation structure. This class is "virtual",
having four "real" classes, corresponding to specific spatial
correlation structures, associated with it: `corExp`

,
`corGaus`

, `corLin`

, `corRatio`

, and
`corSpher`

. The returned object will inherit from one of these
"real" classes, determined by the `type`

argument, and from the
"virtual" `corSpatial`

class. Objects created using this
constructor must later be initialized using the appropriate
`Initialize`

method.

corSpatial(value, form, nugget, type, metric, fixed)

`value` |
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 effect" (one minus the
correlation 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 effect of 0.1
being assigned to the parameters when `object` is initialized. |

`form` |
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. |

`nugget` |
an optional logical value indicating whether a nugget
effect is present. Defaults to `FALSE` . |

`type` |
an optional character string specifying the desired type of
correlation structure. Available types include `"spherical"` ,
`"exponential"` , `"gaussian"` , `"linear"` , and
`"rational"` . See the documentation on the functions
`corSpher` , `corExp` , `corGaus` , `corLin` , and
`corRatio` 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"` . |

`metric` |
an optional character string specifying the distance
metric to be used. The currently available options are
`"euclidean"` 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 `"euclidean"` . |

`fixed` |
an optional logical value indicating whether the
coefficients should be allowed to vary in the optimization, or kept
fixed at their initial value. Defaults to `FALSE` , in which case
the coefficients are allowed to vary. |

an object of class determined by the `type`

argument and also
inheriting from class `corSpatial`

, representing a spatial
correlation structure.

Jose Pinheiro Jose.Pinheiro@pharma.novartis.com and Douglas Bates bates@stat.wisc.edu

Cressie, N.A.C. (1993), "Statistics for Spatial Data", J. Wiley & Sons. Venables, W.N. and Ripley, B.D. (1997) "Modern Applied Statistics with S-plus", 2nd Edition, Springer-Verlag. Littel, Milliken, Stroup, and Wolfinger (1996) "SAS Systems for Mixed Models", SAS Institute.

`corExp`

, `corGaus`

,
`corLin`

, `corRatio`

, `corSpher`

,
`Initialize.corStruct`

, `dist`

sp1 <- corSpatial(form = ~ x + y + z, type = "g", metric = "man")

[Package *nlme* version 3.1-57 Index]