logistic5_fn {drda}R Documentation

5-parameter logistic function


Evaluate at a particular set of parameters the 5-parameter logistic function.


logistic5_fn(x, theta)



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.


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

[Package drda version 2.0.3 Index]