polynomial.js

Polynomial.js is a very simple and small library that helps you calculate polynomial coefficients from points and calculating points based on the curve they represent.

It is based on this StackOverflow answer: http://stackoverflow.com/a/9861559

Installation

Simply use npm or yarn to install the package:

npm install polynomial.js

yarn install polynomial.js

Notes

• All points supplied to the library must be objects with an x- and a y-property.
• To help you with this, you can use the exported class Point (require("polynomial.js").Point). Its' constructor will create such an object for you. It will throw a TypeError if a non-numerical value is supplied.
• Calculating all values from 0 to 100 with the above curve would yield these points: https://pastebin.com/Ucz92TTe

Example

const Curve = require("polynomial.js").Curve;

let points = [
    new Point(0, 5),
    new Point(9, 10),
    new Point(20, -3),
    new Point(50, 23123),
];

let curve = new Curve(points);

let y = curve.compute(5); // 130.03044

Manual API

To create the coefficients array, pass an array with all your points into the method calculatePolynomialCoefficients, like this:

const Polynomial = require("polynomial.js");
const Point = Polynomial.Point;

let points = [
    new Point(0, 5),
    new Point(9, 10),
    new Point(20, -3),
    new Point(50, 23123),
];

let coefficients = Polynomial.calculatePolynomialCoefficients(points);

To calculate a point using those coefficients you can use the method calculateValueForPolynomial:

let y = Polynomial.calculateValueForPolynomial(5, coefficients);

To confirm that this actually works you can just input your original x values, and should receive your original y values:

points.forEach((point) => {
    let y = Polynomial.calculateValueForPolynomial(point.x, coefficients);
    console.log(point.y === y);
});

Tests

To run the tests, simply type npm run test. For coverage run npm run cover. istanbul, mocha and chai are included as dev dependencies.

Credits

Many thanks to:

• Daniel Fischer on StackOverflow. He wrote all the code that makes this library work, I just gave it a nice API and published it. All credit goes to him!
• Tobias Rahloff helped me out with tests and all that. Without him I most likely would have never published this!