Alternative Asymptotic Regression Model with an Offset

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 input when response is zero.

Description

This selfStart model evaluates the alternative asymptotic regression function and its gradient. It has an initial attribute that will evaluate initial estimates of the parameters Asym, lrc, and c0 for a given set of data.

Value

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, as opposed to expressions or explicit numerical values, the gradient matrix with respect to these names is attached as an attribute named gradient.

Author(s)

Jose Pinheiro and Douglas Bates

See Also

nls, selfStart

Examples

library( lme )
data( CO2 )
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


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