code: def _rlFindStart(rl,lz,pot,lower=False):
      
      rtry= 2.*rl
      while (2.*lower-1.)*_rlfunc(rtry,lz,pot) > 0.:
          if lower:
              rtry/= 2.
          else:
              rtry*= 2.
      return rtry
docs: find a starting interval for rl