fn_logistic: Logistic function

In flexFitR: Flexible Non-Linear Least Square Model Fitting

Logistic function

Description

A standard logistic function commonly used to model sigmoidal growth. The curve rises from near zero to a maximum value k, with inflection point at t0 and growth rate a.

Usage

fn_logistic(t, a, t0, k)

Arguments

t	A numeric vector of input values (e.g., time).
a	The growth rate (steepness of the curve). Higher values lead to a steeper rise.
t0	The time of the inflection point (midpoint of the transition).
k	The upper asymptote or plateau (maximum value as t -> Inf).

Details

f(t; a, t0, k) = \frac{k}{1 + e^{-a(t - t_0)}}

This is a classic sigmoid (S-shaped) curve that is symmetric around the inflection point t0.

Value

A numeric vector of the same length as t, representing the logistic function values.

Examples

library(flexFitR)
plot_fn(
  fn = "fn_logistic",
  params = c(a = 0.199, t0 = 47.7, k = 100),
  interval = c(0, 108),
  n_points = 2000
)

flexFitR documentation built on April 16, 2025, 5:09 p.m.