SSasympOff {stats}
Self-Starting Nls Asymptotic Regression Model with an Offset
Description
This selfStart model evaluates an alternative parametrization of the asymptotic regression function and the gradient with respect to those parameters. It has an initial attribute that creates initial estimates of the parameters Asym, lrc, and c0.
Usage
SSasympOff(input, Asym, lrc, c0)
Arguments
- input
- a numeric vector of values at which to evaluate the model.
- Asym
- a numeric parameter representing the horizontal asymptote on the right side (very large values of
input). - lrc
- a numeric parameter representing the natural logarithm of the rate constant.
- c0
- a numeric parameter representing the
inputfor which the response is zero.
Values
a numeric vector of the same length as input. It is the value of the expression Asym*(1 - exp(-exp(lrc)*(input - c0))). If all of the arguments Asym, lrc, and c0 are names of objects, the gradient matrix with respect to these names is attached as an attribute named gradient.
See Also
nls, selfStart; example(SSasympOff) gives graph showing the SSasympOff parametrization, where phi_1 is Asymp, phi_3 is c0.
Examples
CO2.Qn1 <- CO2[CO2$Plant == "Qn1", ] SSasympOff(CO2.Qn1$conc, 32, -4, 43) # response only Asym <- 32; lrc <- -4; c0 <- 43 SSasympOff(CO2.Qn1$conc, Asym, lrc, c0) # response and gradient getInitial(uptake ~ SSasympOff(conc, Asym, lrc, c0), data = CO2.Qn1) ## Initial values are in fact the converged values fm1 <- nls(uptake ~ SSasympOff(conc, Asym, lrc, c0), data = CO2.Qn1) summary(fm1)
Documentation reproduced from R 2.15.3. License: GPL-2.