         centerOn = value
         return self
     }
-    
-    private var needsUpdate: Bool = false
     
     public var bounds: CGRect {
         guard self.nodes.count > 0 else { return CGRectZero }

            step()
            closure(nodes)
            needsUpdate = false
        }
    }
    

        return self
    }
    
    private(set) public var energyThreshold: CGFloat = 0.01
    public func energyThreshold(value: CGFloat) -> Graph {
        energyThreshold = value
        return self
    }
    
    private(set) public var maxVelocity: CGFloat = 1
    public func maxVelocity(value: CGFloat) -> Graph {
        maxVelocity = value
