code: def toLinear(self):
          
          orbSetupKwargs= {'ro':None,
                           'vo':None,
                           'zo':self._orb._zo,
                           'solarmotion':self._orb._solarmotion}
          if self._orb._roSet:
              orbSetupKwargs['ro']= self._orb._ro
          if self._orb._voSet:
              orbSetupKwargs['vo']= self._orb._vo
          if len(self._orb.vxvv) == 6 or len(self._orb.vxvv) == 5:
              vxvv= [self._orb.vxvv[3],self._orb.vxvv[4]]
          else:
              raise AttributeError("planar or linear Orbits do not have the toPlanar attribute")
          return Orbit(vxvv=vxvv,**orbSetupKwargs)
docs: NAME:
  
             toLinear
  
          PURPOSE:
  
             convert a 3D orbit into a 1D orbit (z)
  
          INPUT:
  
             (none)
  
          OUTPUT:
  
             linear Orbit
  
          HISTORY:
  
             2010-11-30 - Written - Bovy (NYU)