<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def lbnd(self):
 """ the lower bound vector while respecting log transform Returns ------- lbnd : pandas.Series """

        if not self.istransformed:
            return self.pst.parameter_data.parlbnd.copy()
        else:
            lb = self.pst.parameter_data.parlbnd.copy()
            lb[self.log_indexer] = np.log10(lb[self.log_indexer])
            return lb