def initialize(self, length=None):
        """see ``__init__``"""
        if length is None:
            length = len(self.bounds)
        max_i = min((len(self.bounds) - 1, length - 1))
        self._lb = array([self.bounds[min((i, max_i))][0]
                          if self.bounds[min((i, max_i))][0] is not None
                          else -np.Inf
                          for i in xrange(length)], copy=False)
        self._ub = array([self.bounds[min((i, max_i))][1]
                          if self.bounds[min((i, max_i))][1] is not None
                          else np.Inf
                          for i in xrange(length)], copy=False)
        lb = self._lb
        ub = self._ub
        # define added values for lower and upper bound
        self._al = array([min([(ub[i] - lb[i]) / 2, (1 + np.abs(lb[i])) / 20])
                             if isfinite(lb[i]) else 1 for i in rglen(lb)], copy=False)
        self._au = array([min([(ub[i] - lb[i]) / 2, (1 + np.abs(ub[i])) / 20])
                             if isfinite(ub[i]) else 1 for i in rglen(ub)], copy=False)
see ``__init__``