docs: def density_profile(self,ixaxis='mass',ifig=None,colour=None,label=None,fname=None):
          '''
          Plot density as a function of either mass coordiate or radius.
  
          Parameters
          ----------
          ixaxis : string
              'mass' or 'radius'
              The default value is 'mass'
          ifig : integer or string
              The figure label
              The default value is None
          colour : string
              What colour the line should be
              The default value is None
          label : string
              Label for the line
              The default value is None
          fname : integer
              What cycle to plot from (if SE output)
              The default value is None
          '''
  
          pT=self._classTest()
  
          # Class-specific things:
          if pT is 'mesa_profile':
              x = self.get(ixaxis)
              if ixaxis is 'radius':
                  x = x*ast.rsun_cm
              y = self.get('logRho')
          elif pT is 'se':
              if fname is None:
                  raise IOError("Please provide the cycle number fname")
              x = self.se.get(fname,ixaxis)
              y = np.log10(self.se.get(fname,'rho'))
          else:
              raise IOError("Sorry. the density_profile method is not available \
                            for this class")
  
          # Plot-specific things:
          if ixaxis is 'radius':
              x = np.log10(x)
              xlab='$\log_{10}(r\,/\,{\\rm cm})$'
          else:
              xlab='${\\rm Mass}\,/\,M_\odot$'
  
          if ifig is not None:
              pl.figure(ifig)
          if label is not None:
              if colour is not None:
                  pl.plot(x,y,color=colour,label=label)
              else:
                  pl.plot(x,y,label=label)
              pl.legend(loc='best').draw_frame(False)
          else:
              if colour is not None:
                  pl.plot(x,y,color=colour)
              else:
                  pl.plot(x,y)
  
          pl.xlabel(xlab)
          pl.ylabel('$\log_{10}(\\rho\,/\,{\\rm g\,cm}^{-3})$')