Evaluate at a particular set of parameters the 5-parameter logistic function.
logistic5_fn(x, theta)Numeric vector of the same length of x with the values of the
logistic function.
numeric vector at which the logistic function is to be evaluated.
numeric vector with the five parameters in the form
c(alpha, delta, eta, phi, nu).
The 5-parameter logistic function f(x; theta) is defined here as
g(x; theta) = 1 / (1 + nu * exp(-eta * (x - phi)))^(1 / nu)
f(x; theta) = alpha + delta g(x; theta)
where theta = c(alpha, delta, eta, phi, nu), eta > 0, and nu > 0.
When delta is positive (negative) the curve is monotonically increasing
(decreasing). When x -> -Inf the value of the function is alpha while the
value of the function for x -> Inf is alpha + delta .
Parameter alpha is the value of the function when x -> -Inf.
Parameter delta is the (signed) height of the curve.
Parameter eta represents the steepness (growth rate) of the curve.
Parameter phi is related to the mid-value of the function.
Parameter nu affects near which asymptote maximum growth occurs.