SSRichards: Richards Growth Model

In NRAIA: Data sets from "Nonlinear Regression Analysis and Its Applications"

Description

This selfStart model evaluates the Richards growth model function and its gradient. It has an initial attribute that creates initial estimates of the parameters Asym, xmid, scal and lpow.

Usage

SSRichards(input, Asym, xmid, scal, lpow)

Arguments

input	a numeric vector of values at which to evaluate the model.
Asym	a numeric parameter representing the asymptote.
xmid	a numeric parameter representing the x value at the inflection point of the curve. The value of SSRichards will be Asym/2 at xmid.
scal	a numeric scale parameter on the input axis.
lpow	the natural logarithm of the inverse of the power to which the denominator is raised.

Value

a numeric vector of the same length as input. It is the value of the expression Asym*(1+exp((xmid-input)/scal))^(-exp(-lpow)). If all of the arguments Asym, xmid, scal and lpow are names of objects, the gradient matrix with respect to these names is attached as an attribute named gradient.

See Also

nls, selfStart

Examples

summary(fm1 <- nls(Length ~ SSRichards(Time, Asym, xmid, scal, lpow), Leaves))

NRAIA documentation built on May 2, 2019, 4:52 p.m.