nlme (version 3.1-31)

corRatio: Rational Quadratic Correlation Structure

Description

This function is a constructor for the corRatio class, representing a rational quadratic spatial correlation structure. Letting $d$ denote the range and $n$ denote the nugget effect, the correlation between two observations a distance $r$ apart is $(r/d)^2/(1+(r/d)^2)$ when no nugget effect is present and $(1-n)(r/d)^2/(1+(r/d)^2)$ when a nugget effect is assumed. Objects created using this constructor need to be later initialized using the appropriate Initialize method.

Usage

corRatio(value, form, nugget, metric, fixed)

Value

an object of class corRatio, also inheriting from class corSpatial, representing a rational quadratic spatial correlation structure.

References

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.

See Also

Initialize.corStruct, dist

Examples

sp1 <- corRatio(form = ~ x + y + z)