SSexpoGrowth: Exponential growth function

In statforbiology: Tools for Data Analyses in Biology

Exponential growth function

Description

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

Usage

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

Arguments

predictor	a numeric vector of values at which to evaluate the model.
init	model parameter: response at predictor = 0
k	model parameter: growth rate
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 growth is given by the following function:

f(x) = \textrm{C0} \cdot \exp ( k x )\}

Value

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

Note

DRC.expoGrowth() 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

library(statforbiology)
Time <- 1:20
Resp <- c(0.18, 0.64, 1.14, 0.67, 0.32, 0.86, 0.70, 0.73, 0.89, 0.48,
    2.20, 1.03, 1.14, 2.14, 1.31, 2.08, 1.85, 1.47, 1.98, 1.30)
model <- drm(Resp ~ Time, fct = DRC.expoGrowth())
summary(model)
model2 <- nls(Resp ~ NLS.expoGrowth(Time, a, b))
summary(model2)

statforbiology documentation built on Oct. 30, 2024, 9:13 a.m.