Five-parameter Weibull type 2 model with lag time

A five-parameter Weibull type 2 model extended with a lag time parameter t0. The model is given by the expression $$f(x) = c + (d - c)(1 - \exp(-\exp(b(\log(x - t0) - \log(e)))))$$ for $x > t0$ and $f(x) = c$ otherwise.

Usage

weibull2x(
  fixed = rep(NA, 5),
  names = c("b", "c", "d", "e", "t0"),
  method = c("1", "2", "3", "4"),
  ssfct = NULL,
  fctName,
  fctText
)

Arguments

fixed: numeric vector of length 5. Specifies which parameters are fixed and at what value. Use NA for parameters that should be estimated (default is rep(NA, 5)).
names: character vector of length 5 giving the names of the parameters (default is c("b", "c", "d", "e", "t0")).
method: character string indicating the self starter method to use. One of "1", "2", "3", or "4".
ssfct: a self starter function. If NULL (default), a built-in self starter is used.
fctName: optional character string specifying the function name (used internally).
fctText: optional character string specifying the function description (used internally).

Value

A list of class "Weibull-2" containing the nonlinear function, self starter function, and parameter names.

Details

The lag time parameter t0 cannot be fixed.

Author

Christian Ritz