logistic4_fn {drda} R Documentation

## 4-parameter logistic function

### Description

Evaluate at a particular set of parameters the 4-parameter logistic function.

### Usage

logistic4_fn(x, theta)


### Arguments

 x numeric vector at which the logistic function is to be evaluated. theta numeric vector with the four parameters in the form c(alpha, beta, eta, phi).

### Details

The 4-parameter logistic function ⁠f(x; theta)⁠ is defined here as

alpha + (beta - alpha) / (1 + exp(-eta * (x - phi)))

where theta = c(alpha, beta, eta, phi), alpha is the lower horizontal asymptote, beta > alpha is the upper horizontal asymptote, eta is the steepness of the curve or growth rate (also known as the Hill coefficient), and phi is the value of x at which the curve is equal to its mid-point.

### Value

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

[Package drda version 1.0.0 Index]