R: Asymptotic Regression Model through the Origin

SSasympOrig {nls} | R Documentation

## Asymptotic Regression Model through the Origin

### Description

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

### Usage

    SSasympOrig(input, Asym, lrc)

### Arguments

`input` | a numeric vector of values at which to evaluate the model.
`Asym` | a numeric parameter representing the horizontal asymptote.
`lrc` | a numeric parameter representing the natural logarithm of the rate constant.

### Value

a numeric vector of the same length as `input`. It is the value of the expression `Asym*(1 - exp(-exp(lrc)*input))`. If all of the arguments `Asym` and `lrc` 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

### See Also

`nls`, `selfStart`

### Examples

    data( Loblolly )
    Lob.329 <- Loblolly[ Loblolly$Seed == "329", ]
    SSasympOrig( Lob.329$age, 100, -3.2 )  # response only
    Asym <- 100; lrc <- -3.2
    SSasympOrig( Lob.329$age, Asym, lrc ) # response and gradient
    getInitial(height ~ SSasympOrig(age, Asym, lrc), data = Lob.329)
    ## Initial values are in fact the converged values
    fm1 <- nls(height ~ SSasympOrig( age, Asym, lrc), data = Lob.329)
    summary(fm1)

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