permjs

A library providing mathematical permutation, combination, and factorial operations.

Installation

Using npm:

npm install --save permjs

Usage

Permutation

Purpose

Finds the possible orders of n objects taken r at a time.

Mathmatical formula

nPr = n!/(n - r)!

Implementation

const { permutation } = require('permjs');

permutation(5, 2); // 5 nPr 2 => 20

Combination

Purpose

Finds the possible sets (without regard to order) of n objects taken r at a time.

Mathematical Formula

nCr = n!/(n - r)!r!

Implementation

const { combination } = require('permjs');

combination(5, 2); // 5 nCr 2 => 10

Factorial

Purpose

Finds a number multipled by all integers smaller than it, down to 1. For example,

5! = 5 * 4 * 3 * 2 * 1 = 120

Mathematical Formula

n! = n * (n - 1) * (n - 2) ... * 1

Implementation

const { factorial } = require('permjs');

factorial(5); // 5! => 120

Pascal's Triangle

Purpose

Gives the binomial coefficients of the binomial power (a + b)^n

Mathematical Formula

Takes the following form:

row[0]:          1
row[1]:         1 1
row[2]:        1 2 1
row[3]:       1 3 3 1
row[4]:      1 4 6 4 1
row[5]:    1 5 10 10 5 1

...etc

Implementation

const { pascal } = require('permjs');

pascal(5); // row[5] => [1, 5, 10, 10, 5, 1]