R: The five-parameter log-logistic function

LL.5 {drc} | R Documentation

## The five-parameter log-logistic function

### Description

'LL.5' and 'LL2.5' provide the five-parameter log-logistic function, self starter function and names of the parameters.

### Usage

      LL.5(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"), ...)

      l5(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"), ...)

      LL2.5(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"), ...)

### Arguments

`fixed` | numeric vector. Specifies which parameters are fixed and at what value they are fixed. NAs for parameter that are not fixed.
`names` | a vector of character strings giving the names of the parameters. The default is reasonable.
`...` | Additional arguments (see `llogistic`).

### Details

The five-parameter logistic function is given by the expression

f(x) = c + \frac{d-c}{(1+\exp(b(\log(x)-\log(e))))^f}

or in another parameterisation

f(x) = c + \frac{d-c}{(1+\exp(b(\log(x)-e)))^f}

The function is asymmetric for f different from 1.

### Value

See `llogistic`.

### Note

This function is for use with the function `drm`.

### Author(s)

Christian Ritz

### References

Finney, D. J. (1979) Bioassay and the Practise of Statistical Inference, Int. Statist. Rev., 47, 1–12.

### See Also

Related functions are `LL.4` and `LL.3`.

### Examples

    ryegrass.m1 <- drm(rootl ~ conc, data = ryegrass, fct = LL.5())
    summary(ryegrass.m1)

[Package drc version 3.0-1 Index]