ramps (version 0.6.18)

corRExp2: Non-Separable Exponential Spatio-Temporal Correlation Structure

Description

This function is a constructor for the 'corRExp2' class, representing a non-separable spatial correlation structure. Letting \(rs\) denote the spatial range, \(rt\) the temporal range, and \(lambda\) the space-time interaction, the correlation between two observations a distance \(d\) apart in space and \(t\) in time is \(\exp(-d/rs - t/rt - \lambda (d/rs) (t/rt))\).

Usage

corRExp2(value = numeric(0), form = ~ 1,
            metric = c("euclidean", "maximum", "manhattan", "haversine"),
            radius = 3956)

Value

Object of class 'corRExp2', inheriting from class 'corRSpatioTemporal', representing a non-separable spatial correlation structure.

Arguments

value

optional numeric vector of three parameter values for the exponential correlation structure, corresponding to the “spatial range”, “temporal range”, and “space-time interaction”. The range parameter values must be greater than zero, and the interaction greater than or equal to zero. Defaults to numeric(0), which results in ranges of 90% of the minimum distances and an interaction of 0 being assigned to the parameters when object is initialized.

form

one-sided formula of the form ~ S1+...+Sp+T, specifying spatial covariates S1 through Sp and the times T at which measurement were taken.

metric

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; "manhattan" for the sum of the absolute differences; and "haversine" for the great-circle distance (miles) between longitude/latitude coordinates. Partial matching of arguments is used, so only the first three characters need to be provided. Defaults to "euclidean".

radius

radius to be used in the haversine formula for great-circle distance. Defaults to the Earth's radius of 3,956 miles.

Author

Brian Smith

References

Cressie, N. and Huang, H.-C. (1993) “Classes of Nonseperable, Spatio-Temporal Stationary Covariance Functions”, Journal of the American Statistical Association, 94, 1330-1340.

See Also

corRClasses

Examples

sp1 <- corRExp2(form = ~ x + y + t)

spatDat <- data.frame(x = (0:4)/4, y = (0:4)/4, t=(0:4)/4)

cs1Exp <- corRExp2(c(1, 1, 1), form = ~ x + y + t)
cs1Exp <- Initialize(cs1Exp, spatDat)
corMatrix(cs1Exp)

cs2Exp <- corRExp2(c(1, 1, 1), form = ~ x + y + t, metric = "man")
cs2Exp <- Initialize(cs2Exp, spatDat)
corMatrix(cs2Exp)