doublePendulum

#to run, use processing 3 in python mode. Also make sure this file is saved as "doublePendulum.pyde" in a folder called "doublePendulum"
class DoublePendulum:
    def __init__(self,th1,th2,g=1,dt=1):
        self.th1=th1%TWO_PI
        self.th2=th2%TWO_PI
        self.om1=0
        self.om2=0
        self.g=g
        self.dt=dt
    def step(self):
        temp=-3*self.g*sin(self.th1)
        temp-=self.g*sin(self.th1-2*self.th2)
        temp-=2*sin(self.th1-self.th2)*(self.om2**2+cos(self.th1-self.th2)*self.om1**2)
        omPrime1=temp/(3-cos(2*self.th1-2*self.th2))
        temp=2*self.om1**2+2*self.g*cos(self.th1)+cos(self.th1-self.th2)*self.om2**2
        omPrime2=temp*2*sin(self.th1-self.th2)/(3-cos(2*self.th1-2*self.th2))

        self.om1+=self.dt*omPrime1
        self.om2+=self.dt*omPrime2
        self.th1=(self.th1+self.dt*self.om1)%TWO_PI
        self.th2=(self.th2+self.dt*self.om2)%TWO_PI

    def show(self,x0,y0,r=20,c=color(255)):
        stroke(c)
        strokeWeight(2)
        x1,y1=x0+r*cos(self.th1+HALF_PI),y0+r*sin(self.th1+HALF_PI)
        x2,y2=x1+r*cos(self.th2+HALF_PI),y1+r*sin(self.th2+HALF_PI)
        line(x0,y0,x1,y1)
        line(x1,y1,x2,y2)
        noStroke()
        fill(255)
        ellipse(x1,y1,3,3)
        ellipse(x2,y2,3,3)

def setup():
    global dp,gridSize
    size(728,728)
    #size(200,200)
    colorMode(HSB)
    gridSize=width
    dp=[[DoublePendulum(TWO_PI*(1-float(i)/gridSize),TWO_PI*j/gridSize,dt=0.01) for j in range(gridSize)] for i in range(gridSize)]
def draw():
    background(255)
    img=createImage(gridSize,gridSize,HSB)
    img.loadPixels()
    for i,row in enumerate(dp):
        for j,p in enumerate(row):
            p.step()
            x=cos(p.th1)+cos(p.th2)
            y=sin(p.th1)+sin(p.th2)
            if x==0: arg=HALF_PI
            else: arg=atan(y/x)
            r=sqrt(x**2+y**2)
            img.pixels[i+j*img.width]=color((arg%PI)*255/PI,255,r*255/2)
    img.updatePixels()
    image(img,0,0)
    #dp[mouseX][mouseY].show(mouseX,mouseY) #show's a tiny pendulum underneath the mouse cursor for the pixel the cursor is over
    #saveFrame("frames\######.png")