docs: def getPDF(self):
          '''Function that gets vectors of the pdf and target at the last design
          evaluated.
  
          :return: tuple of q values, pdf values, target values
          '''
  
          if hasattr(self, '_qplot'):
  
              return self._qplot, self._hplot, self._tplot
  
          else:
              raise ValueError('''The metric has not been evaluated at any
                      design point so the PDF cannot get obtained''')