from visual import *
## deflate G to keep gravitational force from Sun constant
G=6.673e-11

## Force on a due to b
def force(a,b):
    diff=b.pos-a.pos
    return G*b.mass*a.mass*norm(diff)/pow(diff.mag,2.0)

## Finds acceleration of a due to all objects b

def totalacc(a,objlist):
    sum_acc=vector(0,0,0)
    for b in objlist:
        if (a!=b):
            sum_acc=sum_acc+force(a,b)/a.mass
    return sum_acc

## updates positions and track of each object

def update(objlist, dt):
    for i in objlist:
        i.acc=totalacc(i,objlist)
    for i in objlist:
        i.pos=i.pos+dt*i.velocity+i.acc*dt*dt*0.5
        i.track.append(pos=i.pos)
    for i in objlist:
        i.velocity=i.velocity+(i.acc+totalacc(i,objlist))*dt*0.5