bash-logistic-function

An implementation of the logistic function written in GNU bash and GNU basic calculator (bc). It requires four parameters (-x, -m, -L, -k) to output the value of f(x). If there is an error, the function exits with status 1; otherwise, it exists with status 0. (Errors won't generate any message unless the function is called in debug mode with the argument -d.)

This code was meant to be used programatically to output values of a given logistic model across values of a random variable X. See Examples.

Usage

./logistic-function -h

Usage:
  ./logistic-function -x VALUE -m VALUE -L VALUE -k VALUE [OPTIONS]

  Logistic function:
    -x  real*  value of a variable X
    -m  real*  m = x0: Midpoint of X
    -L  real*  max value of f(x)
    -k  real*  growth rate

  * acceptable inputs:
    integers:       ..., -1, 0, 1, ...
    fractions:      ..., -1/2, -.25, 0, .25, 1/2, ...
    positive exps:  ..., "-(2^2)", 0, 2^2, ...
    natural exps:   "e(VALUE)"
    natural logs:   "l(VALUE)"
    square roots:   "sqrt(VALUE)"
    sines:          "s(VALUE)"
    cosines:        "c(VALUE)"
    arctangents:    "a(VALUE)"

  Options:
    -d       enable debug messages.
    -h       show this help message.
    -s  int  # of decimals to compute f(x). default: 20.
    -S  int  # of decimals in the output. default: 2.

  Example:
    logistic-function -x .5 -m 0 -L 1 -k 1 -s 10 -S 4

Author: cgomesu
Repo: https://github.com/cgomesu/bash-logistic-function

Demo

Examples

For the examples below, it was assumed that logistic-function is in the current user's $PATH (e.g., /usr/local/bin). In addition, the logistic model was always the standard logistic sigmoid function with parameters m = 0, L = 1, and k = 1:

If test

Test if a value of X (provided as the first argument) returns a valid status

#!/bin/bash
if logistic-function -x "$1" -m 0 -L 1 -k 1 &>/dev/null; then
  # do something if valid
else
  # do something else
fi
exit 0

For loop

Output values of f(x) for x = -1 to x = 1 in .1 increments

#!/bin/bash
# in GNU systems, make use of seq to handle non-integers in a sequence
for x in $(seq '-1' .1 1); do logistic-function -x "$x" -m 0 -L 1 -k 1; done
exit 0