VGAM (version 0.9-1)

Opt: Maxima

Description

Generic function for the optima (or optimums) of a model.

Usage

Opt(object, ...)

Arguments

object

An object for which the computation or extraction of an optimum (or optima) is meaningful.

...

Other arguments fed into the specific methods function of the model. Sometimes they are fed into the methods function for Coef.

Value

• The value returned depends specifically on the methods function invoked.

Details

Different models can define an optimum in different ways. Many models have no such notion or definition.

Optima occur in quadratic and additive ordination, e.g., CQO or UQO or CAO. For these models the optimum is the value of the latent variable where the maximum occurs, i.e., where the fitted value achieves its highest value. For quadratic ordination models there is a formula for the optimum but for additive ordination models the optimum must be searched for numerically. If it occurs on the boundary, then the optimum is undefined. At an optimum, the fitted value of the response is called the maximum.

References

Yee, T. W. (2004) A new technique for maximum-likelihood canonical Gaussian ordination. Ecological Monographs, 74, 685--701.

Yee, T. W. (2006) Constrained additive ordination. Ecology, 87, 203--213.

See Also

Opt.qrrvglm, Max, Tol.

Examples

set.seed(111)  # This leads to the global solution
hspider[,1:6] <- scale(hspider[,1:6]) # Standardized environmental vars
# vvv p1 = cqo(cbind(Alopacce, Alopcune, Alopfabr, Arctlute, Arctperi,
# vvv                Auloalbi, Pardlugu, Pardmont, Pardnigr, Pardpull,
# vvv                Trocterr, Zoraspin) ~
# vvv          WaterCon + BareSand + FallTwig + CoveMoss + CoveHerb + ReflLux,
# vvv          Bestof = 2,
# vvv          fam = quasipoissonff, data = hspider, Crow1positive=FALSE)
# vvv Opt(p1)

index <- 1:ncol(depvar(p1))
persp(p1, col = index, las = 1, lwd = 2, main = "Vertical lines at the optima")
abline(v = Opt(p1), lty = 2, col = index)