richards-package {richards}R Documentation

The package provides selfStarts and functions for Richards curves

Description

selfStart models and functions for Richards curves:

SSrichardsSimple <- selfStart( ~ d + (a - d) / (1 + (2^ny-1) * (input / x50)^b)^(1/ny), function (mCall, data, LHS) initialRichards(mCall, data, LHS), c("a", "d", "b", "x50", "ny"))

Why a package for this one line?

The function for the initial values is a call to the selfStart model SSfpl of the four parameter logistic function.

selfStart models for Richards curves with specific fixed values of the shape parameter ny are also given. For these a Richards function described by ny and the same asymptotes, location and slope parameters as for a fitted four parameter logistic function is found and used for the initial value.

If ny is negative then 1 + (2^ny-1)*(input/x50)^b can also be negative, and then this value cannot be raised to 1/ny (unless 1/ny is an integer). 'Modified' selfStart models are given to handle this situation.

Details

Package: richards
Type: Package
Version: 0.4.5
Date: 2008-09-01
License: GPL Version 2 or later

Author(s)

Jens Henrik Badsberg

Maintainer: Jens Henrik Badsberg <september2008richards@badsberg.eu>

References

Richards, F.J. 1959: A flexible growth function for empirical use. J. Exp. Bot. 10: 290-300.

http://en.wikipedia.org/wiki/Generalised_logistic_curve.


[Package richards version 0.5.0 Index]