docs: def is_single_trajectory(nc, variable):
      '''
      Returns true if the variable is a single trajectory feature
  
      :param netCDF4.Dataset nc: An open netCDF dataset
      :param str variable: name of the variable to check
      '''
      # x(t), y(t), z(t), t(t)
      # X(t)
      dims = nc.variables[variable].dimensions
      cmatrix = coordinate_dimension_matrix(nc)
  
      for req in ('x', 'y', 't'):
          if req not in cmatrix:
              return False
      t = get_time_variable(nc)
      if cmatrix['x'] != (t,):
          return False
      if cmatrix['x'] != cmatrix['y']:
          return False
      if cmatrix['x'] != cmatrix['t']:
          return False
      if 'z' in cmatrix and cmatrix['x'] != cmatrix['z']:
          return False
      if dims == cmatrix['x']:
          return True
      return False