loglogistic2_fn {drda}R Documentation

2-parameter log-logistic function


Evaluate at a particular set of parameters the 2-parameter log-logistic function.


loglogistic2_fn(x, theta)



numeric vector at which the function is to be evaluated.


numeric vector with the four parameters in the form c(alpha, delta, eta, phi). alpha can only be equal to 0 or 1 while delta can only be equal to 1 or -1.


The 2-parameter log-logistic function ⁠f(x; theta)⁠ is defined here as

⁠g(x; theta) = x^eta / (x^eta + phi^eta)⁠ ⁠f(x; theta) = alpha + delta g(x; theta)⁠

where x >= 0, theta = c(alpha, delta, eta, phi), eta > 0, and phi > 0. Only eta and phi are free to vary (therefore the name) while vector c(alpha, delta) is constrained to be either c(0, 1) (monotonically increasing curve) or c(1, -1) (monotonically decreasing curve).

This function allows values other than 0, 1, -1 for alpha and delta but will coerce them to their proper constraints.


Numeric vector of the same length of x with the values of the log-logistic function.

[Package drda version 2.0.3 Index]