# SSasympOff {stats}

### 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.

### 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 3.0.2. License: GPL-2.