var tween = { 
    easeInQuad: function(pos){ 
      return Math.pow(pos, 2); 
    }, 

    easeOutQuad: function(pos){ 
      return -(Math.pow((pos-1), 2) -1); 
    }, 

    easeInOutQuad: function(pos){ 
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,2); 
      return -0.5 * ((pos-=2)*pos - 2); 
    }, 

    easeInCubic: function(pos){ 
      return Math.pow(pos, 3); 
    }, 

    easeOutCubic: function(pos){ 
      return (Math.pow((pos-1), 3) +1); 
    }, 

    easeInOutCubic: function(pos){ 
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,3); 
      return 0.5 * (Math.pow((pos-2),3) + 2); 
    }, 

    easeInQuart: function(pos){ 
      return Math.pow(pos, 4); 
    }, 

    easeOutQuart: function(pos){ 
      return -(Math.pow((pos-1), 4) -1) 
    }, 

    easeInOutQuart: function(pos){ 
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,4); 
      return -0.5 * ((pos-=2)*Math.pow(pos,3) - 2); 
    }, 

    easeInQuint: function(pos){ 
      return Math.pow(pos, 5); 
    }, 

    easeOutQuint: function(pos){ 
      return (Math.pow((pos-1), 5) +1); 
    }, 

    easeInOutQuint: function(pos){ 
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,5); 
      return 0.5 * (Math.pow((pos-2),5) + 2); 
    }, 

    easeInSine: function(pos){ 
      return -Math.cos(pos * (Math.PI/2)) + 1; 
    }, 

    easeOutSine: function(pos){ 
      return Math.sin(pos * (Math.PI/2)); 
    }, 

    easeInOutSine: function(pos){ 
      return (-.5 * (Math.cos(Math.PI*pos) -1)); 
    }, 

    easeInExpo: function(pos){ 
      return (pos==0) ? 0 : Math.pow(2, 10 * (pos - 1)); 
    }, 

    easeOutExpo: function(pos){ 
      return (pos==1) ? 1 : -Math.pow(2, -10 * pos) + 1; 
    }, 

    easeInOutExpo: function(pos){ 
      if(pos==0) return 0; 
      if(pos==1) return 1; 
      if((pos/=0.5) < 1) return 0.5 * Math.pow(2,10 * (pos-1)); 
      return 0.5 * (-Math.pow(2, -10 * --pos) + 2); 
    }, 

    easeInCirc: function(pos){ 
      return -(Math.sqrt(1 - (pos*pos)) - 1); 
    }, 

    easeOutCirc: function(pos){ 
      return Math.sqrt(1 - Math.pow((pos-1), 2)) 
    }, 

    easeInOutCirc: function(pos){ 
      if((pos/=0.5) < 1) return -0.5 * (Math.sqrt(1 - pos*pos) - 1); 
      return 0.5 * (Math.sqrt(1 - (pos-=2)*pos) + 1); 
    }, 

    easeOutBounce: function(pos){ 
      if ((pos) < (1/2.75)) { 
        return (7.5625*pos*pos); 
      } else if (pos < (2/2.75)) { 
        return (7.5625*(pos-=(1.5/2.75))*pos + .75); 
      } else if (pos < (2.5/2.75)) { 
        return (7.5625*(pos-=(2.25/2.75))*pos + .9375); 
      } else { 
        return (7.5625*(pos-=(2.625/2.75))*pos + .984375); 
      } 
    }, 

    easeInBack: function(pos){ 
      var s = 1.70158; 
      return (pos)*pos*((s+1)*pos - s); 
    }, 

    easeOutBack: function(pos){ 
      var s = 1.70158; 
      return (pos=pos-1)*pos*((s+1)*pos + s) + 1; 
    }, 

    easeInOutBack: function(pos){ 
      var s = 1.70158; 
      if((pos/=0.5) < 1) return 0.5*(pos*pos*(((s*=(1.525))+1)*pos -s)); 
      return 0.5*((pos-=2)*pos*(((s*=(1.525))+1)*pos +s) +2); 
    }, 

    elastic: function(pos) { 
      return -1 * Math.pow(4,-8*pos) * Math.sin((pos*6-1)*(2*Math.PI)/2) + 1; 
    }, 

    swingFromTo: function(pos) { 
      var s = 1.70158; 
      return ((pos/=0.5) < 1) ? 0.5*(pos*pos*(((s*=(1.525))+1)*pos - s)) : 
        0.5*((pos-=2)*pos*(((s*=(1.525))+1)*pos + s) + 2); 
    }, 

    swingFrom: function(pos) { 
      var s = 1.70158; 
      return pos*pos*((s+1)*pos - s); 
    }, 

    swingTo: function(pos) { 
      var s = 1.70158; 
      return (pos-=1)*pos*((s+1)*pos + s) + 1; 
    }, 

    bounce: function(pos) { 
      if (pos < (1/2.75)) { 
        return (7.5625*pos*pos); 
      } else if (pos < (2/2.75)) { 
        return (7.5625*(pos-=(1.5/2.75))*pos + .75); 
      } else if (pos < (2.5/2.75)) { 
        return (7.5625*(pos-=(2.25/2.75))*pos + .9375); 
      } else { 
        return (7.5625*(pos-=(2.625/2.75))*pos + .984375); 
      } 
    }, 

    bouncePast: function(pos) { 
      if (pos < (1/2.75)) { 
        return (7.5625*pos*pos); 
      } else if (pos < (2/2.75)) { 
        return 2 - (7.5625*(pos-=(1.5/2.75))*pos + .75); 
      } else if (pos < (2.5/2.75)) { 
        return 2 - (7.5625*(pos-=(2.25/2.75))*pos + .9375); 
      } else { 
        return 2 - (7.5625*(pos-=(2.625/2.75))*pos + .984375); 
      } 
    }, 

    easeFromTo: function(pos) { 
      if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,4); 
      return -0.5 * ((pos-=2)*Math.pow(pos,3) - 2); 
    }, 

    easeFrom: function(pos) { 
      return Math.pow(pos,4); 
    }, 

    easeTo: function(pos) { 
      return Math.pow(pos,0.25); 
    }, 

    linear:  function(pos) { 
      return pos 
    }, 

    sinusoidal: function(pos) { 
      return (-Math.cos(pos*Math.PI)/2) + 0.5; 
    }, 

    reverse: function(pos) { 
      return 1 - pos; 
    }, 

    mirror: function(pos, transition) { 
      transition = transition || tween.sinusoidal; 
      if(pos<0.5) 
        return transition(pos*2); 
      else 
        return transition(1-(pos-0.5)*2); 
    }, 

    flicker: function(pos) { 
      var pos = pos + (Math.random()-0.5)/5; 
      return tween.sinusoidal(pos < 0 ? 0 : pos > 1 ? 1 : pos); 
    }, 

    wobble: function(pos) { 
      return (-Math.cos(pos*Math.PI*(9*pos))/2) + 0.5; 
    }, 

    pulse: function(pos, pulses) { 
      return (-Math.cos((pos*((pulses||5)-.5)*2)*Math.PI)/2) + .5; 
    }, 

    blink: function(pos, blinks) { 
      return Math.round(pos*(blinks||5)) % 2; 
    }, 

    spring: function(pos) { 
      return 1 - (Math.cos(pos * 4.5 * Math.PI) * Math.exp(-pos * 6)); 
    }, 

    none: function(pos){ 
      return 0 
    }, 

    full: function(pos){ 
      return 1 
    } 
  }