SSasympOff {stats} R Documentation

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 `input` for which the response is zero.

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, the gradient matrix with respect to these names is attached as an attribute named `gradient`.

Author(s)

Jose Pinheiro and Douglas Bates

`nls`, `selfStart`

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 ~ SSasymp( conc, Asym, lrc, c0), data = CO2.Qn1)
## Initial values are in fact the converged values
fm1 <- nls(uptake ~ SSasymp( conc, Asym, lrc, c0), data = CO2.Qn1)
summary(fm1)

```

[Package stats version 2.5.0 Index]