This function provides a very general way of specifying the mean function of the decreasing or incresing Gompertz dose-response or growth curve models.

1 2 3 |

`fixed` |
numeric vector. Specifies which parameters are fixed and at what value they are fixed. NAs for parameter that are not fixed. |

`names` |
vector of character strings giving the names of the parameters (should not contain ":"). The order of the parameters is: b, c, d, e (see under 'Details' for the precise meaning of each parameter). |

`method` |
character string indicating the self starter function to use. |

`ssfct` |
a self starter function to be used. |

`fctName` |
character string used internally by convenience functions (optional). |

`fctText` |
character string used internally by convenience functions (optional). |

The Gompertz model is given by the mean function

* f(x) = c + (d-c)(\exp(-\exp(b(x-e)))) *

and it is a dose-response/growth curve on the entire real axis, that is it is not limited to non-negative values even though this is the range for most dose-response and growth data. One consequence is that the curve needs not reach the lower asymptote at dose 0.

If

*b<0*

the mean function is increasing and it is decreasing for

*b>0*

. The decreasing Gompertz model is not a well-defined dose-response model and other dose-response models such as the Weibull models should be used instead.

Various re-parameterisations of the model are used in practice.

The value returned is a list containing the non-linear function, the self starter function and the parameter names.

The function is for use with the function `drm`

, but typically the convenience functions
`G.2`

, `G.3`

, `G.3u`

, and `G.4`

should be used.

Christian Ritz

Seber, G. A. F. and Wild, C. J. (1989) *Nonlinear Regression*, New York: Wiley \& Sons (p. 331).

The Weibull model `weibull2`

is closely related to the Gompertz model.

Questions? Problems? Suggestions? Tweet to @rdrrHQ or email at ian@mutexlabs.com.

Please suggest features or report bugs with the GitHub issue tracker.

All documentation is copyright its authors; we didn't write any of that.