Evaluate at a particular set of parameters the gradient and Hessian of the 4-parameter logistic function.
logistic4_gradient(x, theta)logistic4_hessian(x, theta)
logistic4_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 logistic function f(x; theta) is defined here as
g(x; theta) = 1 / (1 + exp(-eta * (x - phi)))
f(x; theta) = alpha + delta g(x; theta)
where theta = c(alpha, delta, eta, phi) and eta > 0. When delta is
positive (negative) the curve is monotonically increasing (decreasing).