Evaluate at a particular set of parameters the gradient and Hessian of the log-Gompertz function.
loggompertz_gradient(x, theta)loggompertz_hessian(x, theta)
loggompertz_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 log-Gompertz function f(x; theta) is defined here as
f(x; theta) = alpha + delta exp(-(phi / x)^eta)
where x >= 0, theta = c(alpha, delta, eta, phi), eta > 0, and
phi > 0. By convention we set
f(0; theta) = lim_{x -> 0} f(x; theta) = alpha.