#! /usr/bin/env python
"""
exchangeBoson.py is a program which generates a 3D animation
two spheres exchanging another smaller sphere


Paul Eugenio
PHZ4151C
Feb 1, 2019
"""
from __future__ import division, print_function
import vpython as vp


fermionSize = 0.5
bosonSize=0.1

vp.canvas(width=800, height=800)

# create the spheres
fermi1 = vp.sphere(pos=vp.vector(-2.5,0,0), radius=fermionSize ,color=vp.color.green)
fermi2 = vp.sphere(pos=vp.vector(2.5,0,0), radius=fermionSize ,color=vp.color.yellow)
boson = vp.sphere(pos=vp.vector(0,0,0), radius=bosonSize, color=vp.color.blue)

# initialize time and position of exchange particle
t, dt = 0.0, 0.1
x, v = 0.0, 5
y,z = 0,0

# exchange the smaller sphere forever
while True:
    vp.rate(10)
    t += dt
    if x <-2 or x > 2:
    	v = -v
    x = x + v*dt
    boson.pos.x = x