runge-kutta-4

The fourth order Runge-Kutta integration method.

Introduction

Normal way:

<!-- use the min file -->
<script src="[path]/dist/runge-kutta-4.min.js"></script>

Easy with npm:

$ npm install runge-kutta-4

/**

this is the target differential equations
@param {Array} y It is an unknown function of x which we would like to approximate
@param {Number} x x
@return {Array} dydx The rate at which y changes, is a function of x and of y */ var derives = function(x, y) { // you need to return the integration var dydx = []

dydx[0] = y[0] + y[1] dydx[1] = 2 * y[1] + y[2] dydx[2] = 3 * y[2]

return dydx }

var xStart = 0, yStart = [1, 5, 10], h = 0.0001

var rk4 = new RungeKutta4(derives, xStart, yStart, h)

console.log(rk4.step()) // [ 1.0006001300160015, 5.002000350038337, 10.003000450045004 ]

// console.log(rk4.steps(100)) // [ 1.0613161367179729, 5.2035386394013905, 10.304545339535162 ]

// console.log(rk4.end(0.01)) // [ 1.0613161367179729, 5.2035386394013905, 10.304545339535162 ] // same as steps(100), because steps = xEnd / h `