Evaluate at a particular set of parameters the gradient and Hessian of the 4-parameter log-logistic function.
loglogistic4_gradient(x, theta)loglogistic4_hessian(x, theta)
loglogistic4_gradient_hessian(x, theta)
Gradient or Hessian evaluated at the specified point.
numeric vector at which the function is to be evaluated.
numeric vector with the four parameters in the form
c(alpha, delta, eta, phi).
The 4-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.