R: Self-Starting Nls First-order Compartment Model

SSfol {stats} | R Documentation

## Self-Starting Nls First-order Compartment Model

### Description

This `selfStart` model evaluates the first-order compartment function and its gradient. It has an `initial` attribute that creates initial estimates of the parameters `lKe`, `lKa`, and `lCl`.

### Usage

    SSfol(Dose, input, lKe, lKa, lCl)

### Arguments

`Dose` | a numeric value representing the initial dose.
`input` | a numeric vector at which to evaluate the model.
`lKe` | a numeric parameter representing the natural logarithm of the elimination rate constant.
`lKa` | a numeric parameter representing the natural logarithm of the absorption rate constant.
`lCl` | a numeric parameter representing the natural logarithm of the clearance.

### Value

a numeric vector of the same length as `input`, which is the value of the expression

    Dose * exp(lKe+lKa-lCl) * (exp(-exp(lKe)*input) - exp(-exp(lKa)*input))
        / (exp(lKa) - exp(lKe))

If all of the arguments `lKe`, `lKa`, and `lCl` are names of objects, the gradient matrix with respect to these names is attached as an attribute named `gradient`.

### Author(s)

José Pinheiro and Douglas Bates

### See Also

`nls`, `selfStart`

### Examples

    Theoph.1 <- Theoph[ Theoph$Subject == 1, ]
    with(Theoph.1, SSfol(Dose, Time, -2.5, 0.5, -3)) # response only
    with(Theoph.1, local({  lKe <- -2.5; lKa <- 0.5; lCl <- -3
      SSfol(Dose, Time, lKe, lKa, lCl) # response _and_ gradient
    }))
    getInitial(conc ~ SSfol(Dose, Time, lKe, lKa, lCl), data = Theoph.1)
    ## Initial values are in fact the converged values
    fm1 <- nls(conc ~ SSfol(Dose, Time, lKe, lKa, lCl), data = Theoph.1)
    summary(fm1)

[Package stats version 4.0.5 Index]