SSexpoDecay: Exponential decay function

In OnofriAndreaPG/aomisc: Statistical methods for the agricultural sciences

Exponential decay function

Description

These functions provide the exponential decay function (expoDecay), the exponential decay function with self-starter for the nls function and the exponential decay function with self-starter for the drm function in the drc package.

Usage

  expoDecay.fun(predictor, init, k)
  NLS.expoDecay(predictor, init, k)
  DRC.expoDecay(fixed = c(NA, NA), names = c("init", "k"), ...)

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.

Details

The exponential decay is given by the following function:

f(x) = \textrm{init} \cdot \exp (- k x )\}

Value

expoDecay.fun and NLS.expoDecay return a numeric value, while DRC.expoDecay returns a list containing the nonlinear function, the self starter function and the parameter names.

Note

DRC.expoDecay is for use with the function drm.

Author(s)

Andrea Onofri

References

Ratkowsky, DA (1990) Handbook of nonlinear regression models. New York (USA): Marcel Dekker Inc.

Onofri, A. (2020). A collection of self-starters for nonlinear regression in R. See: https://www.statforbiology.com/2020/stat_nls_usefulfunctions/

Examples

rm(list=ls())
devtools::load_all()
data("degradation")
model <- drm(Conc ~ Time, fct = DRC.expoDecay(),
             data = degradation)
summary(model)
model2 <- nls(Conc ~ NLS.expoDecay(Time, a, b), 
              data = degradation)
summary(model2)

OnofriAndreaPG/aomisc documentation built on Feb. 2, 2023, 12:13 p.m.