Description Usage Arguments Details Value Note Author(s) References See Also Examples

'LL.4' and 'LL2.4' provide the four-parameter log-logistic function, self starter function, names of the parameters and, optionally, first and second derivatives for a faster estimation.

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`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 |

The four-parameter log-logistic function is given by the expression

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

or in another parameterisation (converting the term *\log(e)* into a parameter)

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

The function is symmetric about the inflection point (*e*).

See `llogistic`

.

This function is for use with the function `drm`

.

Christian Ritz and Jens C. Streibig

Seber, G. A. F. and Wild, C. J (1989) *Nonlinear Regression*, New York: Wiley \& Sons (p. 330).

Setting *c=0* yields `LL.3`

. See also `LL.5`

.

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drc documentation built on May 29, 2017, 11:31 a.m.

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