code: function lerp(v, alpha) {
           this._x += (v.x - this._x) * alpha;
           this._y += (v.y - this._y) * alpha;
           this._z += (v.z - this._z) * alpha;
           return this;
         }
docs: Linearly interpolate between this vector and the given one.
  @name lerp
  @memberOf me.ObservableVector3d
  @function
  @param {me.Vector3d|me.ObservableVector3d} v
  @param {Number} alpha distance along the line (alpha = 0 will be this vector, and alpha = 1 will be the given one).
  @return {me.ObservableVector3d} Reference to this object for method chaining