spring with external force

euler, Rk4

by jmchen

HTML

<div id="info">Spring Simulation
 <br/> <a href="javascript:reset();">RESET</a>
 <br/> left click to pull
</div>
<!--div id='eulerM'>Euler</div-->
<div id='RK4M'>RK4</div>
<!--div id='ImEuler'>ImplicitEuler</div-->
<script src="http://cdnjs.cloudflare.com/ajax/libs/three.js/r70/three.min.js"></script>

CSS

#info {
    position: absolute;
    top: 0px;
    width: 100%;
    padding: 10px;
    text-align: center;
    color: #ffff00
}
#eulerM {
    position: absolute;
    top: 40%;
    left: 30%;
    color: white;
}
#RK4M {
    position: absolute;
    top: 50%;
    left: 30%;
    color: cyan;
}
#ImEuler {
    position: absolute;
    top: 80%;
    left: 30%;
    color: yellow;
}
a {
    color: yellow
}
body {
    overflow: hidden;
}

JavaScript

// period T = 2PI sqrt (m/k)
//
var camera, scene, renderer
var mesh, mesh2, mesh3;
var clock = new THREE.Clock();
var x2 = [];
var mouse = new THREE.Vector2();
var m = 1, k = 10, c = 0.53;
var mouseDown = false;
var forceEXT = 0;
var forceLine;

function reset() {
    x2[0] = 20, x2[1] = 0;
}

function deriv(x) {
    var ff = [];
    ff.push(x[1]); // x_dot = v;
    ff.push(-(c * x[1] + k * x[0] - forceEXT) / m);
    return ff;
}

function MidPoint(x, dt) {
    var n = x.length;

    var xcopy = x.slice(0);
    var f = deriv(x);

    // y(x+0.5h)
    for (var i = 0; i < n; i++) {
        xcopy[i] += f[i] * dt / 2;
    }

    f = deriv(xcopy);
    for (var i = 0; i < n; i++) {
        x[i] += f[i] * dt;
    }
}

init();
animate();

function init() {
    scene = new THREE.Scene();

    camera = new THREE.OrthographicCamera(-50, 50, 50, -50, -10, 10);
    camera.position.z = 10;
    scene.add(camera);

    mesh = new THREE.Mesh(new THREE.CircleGeometry(1, 10), new THREE.MeshBasicMaterial());
    mesh2 = mesh.clone();
    scene.add(mesh2);

    var material = new THREE.LineBasicMaterial({
        color: 0x0000ff
    });
    var geometry = new THREE.Geometry();
    geometry.vertices.push(
    new THREE.Vector3(20, 0, 0),
    new THREE.Vector3(-20, 0, 0));
    var border = new THREE.Line(geometry, material);
    scene.add(border);

    geometry = new THREE.Geometry();
    geometry.vertices.push (new THREE.Vector3(), new THREE.Vector3(10,10,0));
    forceLine = new THREE.Line (geometry, new THREE.LineDashedMaterial({color:0xffff00,dashSize: 4, gapSize: 2}));
    scene.add (forceLine);
    forceLine.visible = false;
    
    renderer = new THREE.WebGLRenderer();
    renderer.setSize(window.innerWidth, window.innerHeight);
    renderer.setClearColor(0x888888);

    document.body.appendChild(renderer.domElement);
    window.addEventListener('resize', onWindowResize, false);
	window.addEventListener( 'mousedown', onDocumentMouseDown, false );
//	window.addEventListener(...