るんげくった

ODE

document.getElementById('helloWorld').innerHTML = 'Hello, World!';

var g = 9.8;
var L = 9.8;
var w = 100;
var PI = 3.14159265;

function dprint(s){
    document.getElementById('helloWorld').innerHTML += "<p>" +s+"</p>\n";
}

function Eta(t){ return Math.sin(2*PI*w*t);}
function dEta(t){return 2*PI*w * Math.cos(2*PI*w*t);}
function ddEta(t){
    return -1* (2*PI*w)^2 * Eta(t);
}

function defEq1(t,y,v){
     return v;
}

function defEq2(t,y,v){
    return -1*(g + ddEta(t))/L * Math.sin(y); 
}

var N = 1000;
var h = 0.001; //[s]
var g = 9.8;
var t0=0;
var y0=0; //theta[rad]
var v0=0; //dtheta/dt[rad/t]

dprint(t0+":"+y0+":"+v0);
//var k0=0, k1=0, k2=0, k3=0;
//var l0=0, l1=0, l2=0, l3=0;

for(var i=0; i<N; i++){
    dprint(t0+":"+y0+":"+v0);
    //dprint(y0);
    
    k0 = h * defEq1(t0,y0,v0);
    l0 = h * defEq2(t0,y0,v0);
    
    k1 = h * defEq1(t0+h/2, y0+k0/2, v0+l0/2);
    l1 = h * defEq2(t0+h/2, y0+k0/2, v0+l0/2);
    
    k2 = h * defEq1(t0+h/2, y0+k1/2, v0+l1/2);
    l2 = h * defEq2(t0+h/2, y0+k1/2, v0+l1/2);
    
    k3 = h * defEq1(t0+h, y0+k2, v0+l2);
    l3 = h * defEq2(t0+h, y0+k2, v0+l2);
    
    t0 = t0 + h;
    y0 = y0 + (k0 + 2*k1 + 2*k2 * k3)/6;
    v0 = v0 + (l0 + 2*l1 + 2*l2 * l3)/6;
}