p.constrain {simecol}R Documentation

Transform data between unconstrained and box box-constrained scale

Description

These functions can be used to transform a vector of data or parameters between unconstrained [-Inf, Inf] and box-constrained representation (interval [lower, upper]).

Usage

p.constrain(p, lower = -Inf, upper = Inf, f = 1)
p.unconstrain(p, lower = -Inf, upper = Inf, f = 1)

Arguments

p vector of data (e.g. model parameters),
lower, upper vectors with lower resp. upper bounds used for transformation,
f optional scaling factor.

Details

These functions are employed by fitOdeModel ssqOdeModel in order to be able to use the unconstrained optimizers of optim for constrained optimization. The transformation functions are

p' = tan(pi/2 * (2 * p - upper - lower) / (upper - lower)) / f

and its inverse

p = 1/2 * (upper + lower) + (upper - lower) * arctan(f * p')/pi

.

Value

vector with transformed (resp. back-transformed) values.

References

Reichert, T. (1998) AQUASIM 2.0 User Manual. Computer Program for the Identification and Simulation of Aquatic Systems. Swiss Federal Institute for Environmental Science and Technology (EAWAG), CH - 8600 Duebendorf Switzerland, http://www.aquasim.eawag.ch/e_aquasim_manual.html

See Also

fitOdeModel, ssqOdeModel

Examples

xx <- seq(-100, 100, 2)
plot(xx, yy<-p.constrain(xx, -20, 45), type="l")
points(p.unconstrain(yy, -20, 45), yy, col="red")

[Package simecol version 0.6-1 Index]