drc (version 1.5-5)

logistic: The logistic (Boltzmann) model

Description

The asymmetric logistic (Boltzmann) model for dose-response relationships.

Usage

logistic(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"), fctName, fctText) 

  L.3(fixed = c(NA, NA, NA), names = c("b", "d", "e"))
  L.4(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"))
  L.5(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"))  

  boltzmann(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"), fctName, fctText)

  B.3(fixed = c(NA, NA, NA), names = c("b", "d", "e"))
  B.4(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"))
  B.5(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"))

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 (should not contain ":"). The order of the parameters is: b, c, d, e, f (see under 'Details').

fctName

optional character string used internally by convenience functions.

fctText

optional character string used internally by convenience functions.

Value

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

Details

The default arguments yields the five-parameter logistic mean function given by the expression $$f(x) = c + \frac{d-c}{(1+\exp(b(x - e)))^f}$$ The model is different from the log-logistic models llogistic and llogistic2 where the term $$log(x)$$ is used instead of $$x$$.

Examples

## Fitting the logistic model
m1 <- multdrc(ryegrass, fct = logistic())
summary(m1)

## Fitting an asymmetric logistic model
##  requires installing the package 'NISTnls'
# m2 <- drm(y~x, data = Ratkowsky3, 
# fct = b5(fixed = c(NA, 0, NA, NA, NA)))
# plot(m2)
# summary(m2)  
## okay agreement with NIST values
##  for the two parameters that are the same