Solv.js 💡

Solv.js finds the right input value to a function for a predefined output value. It uses the Steffensen's Method.

Install

npm i --save solv.js

Parameters

The method signature is as follows:

solve = (
  functionToSolveFor: (x: number) => number,
  targetResult: number = 0,
  initialGuess: number = 0, // A guess to speed up the process
  precision: number = 0.01, // Absolute acceptable difference with goal
  maxIterations: number = 100, // Maximum number of iteration before it fails to converge
): number

All function parameters are optional except the func parameter.

Usage

Javascript

// Import the solve function.
var SolvJS = require('solv.js');

// Examples:
var solution1 = SolvJS.solve((x) => x + 7); // -7
var solution2 = SolvJS.solve((x) => x * x + 5 * x + 6); // -1.9995882538671066
var solution3 = SolvJS.solve((x) => x * x + 5 * x + 6, 0, -3); // -3
var solution4 = SolvJS.solve((x) => x * x + 5 * x + 6, 0, 0, Math.pow(10, -9)); // -1.9999999999997717

// A more elaborate example
function costPizzas(meetingParticipants) {
  const numberOfPizzas = Math.ceil(meetingParticipants / 4);
  const pricePerPizza = numberOfPizzas < 4 ? 20.95 : 20.95 * 0.9;
  return numberOfPizzas * pricePerPizza;
}
function costDrinks(meetingParticipants) {
  return meetingParticipants * 4.5;
}

function costMeeting(meetingParticipants) {
  return costPizzas(meetingParticipants) + costDrinks(meetingParticipants);
}
const meetingParticipantsFor250 = SolvJS.solve(costMeeting, 250);

var error1 = SolvJS.solve((x) => 'Hello there'); // Throws an error
var error2 = SolvJS.solve((x) => x * x, -1); // Throws an error

Typescript

// Import the solve function.
import { solve } from 'solv.js';

// Examples:
const solution1 = solve((x) => x + 7); // -7
const solution2 = solve((x) => x * x + 5 * x + 6); // -1.9995882538671066
const solution3 = solve((x) => x * x + 5 * x + 6, 0, -3); // -3
const solution4 = solve((x) => x * x + 5 * x + 6, 0, 0, Math.pow(10, -9)); // -1.9999999999997717

// A more elaborate example
const costPizzas = (meetingParticipants: number) => {
  const numberOfPizzas = Math.ceil(meetingParticipants / 4);
  const pricePerPizza = numberOfPizzas < 4 ? 20.95 : 20.95 * 0.9;
  return numberOfPizzas * pricePerPizza;
};
const costDrinks = (meetingParticipants: number) => meetingParticipants * 4.5;
const costMeeting = (meetingParticipants: number) => {
  return costPizzas(meetingParticipants) + costDrinks(meetingParticipants);
};
const meetingParticipantsFor250 = solve(costMeeting, 250); // 26.225555555555548

const error1 = solve((x) => 'Hello there'); // Throws an error
const error2 = solve((x) => x * x, -1); // Throws an error

Credits

This package is inspired by the package goal-seek.