docs: def checkArgs(args):
      """Checks the arguments and options.
  
      :param args: a :py:class:`argparse.Namespace` object containing the options
                   of the program.
  
      :type args: argparse.Namespace
  
      :returns: ``True`` if everything was OK.
  
      If there is a problem with an option, an exception is raised using the
      :py:class:`ProgramError` class, a message is printed to the
      :class:`sys.stderr` and the program exists with code 1.
  
      """
      # Checking the input files
      if not os.path.isfile(args.mds):
          msg = "{}: no such file".format(args.mds)
          raise ProgramError(msg)
  
      if not os.path.isfile(args.population_file):
          msg = "{}: no such file".format(args.population_file)
          raise ProgramError(msg)
  
      # Checking the chosen components
      if args.xaxis == args.yaxis:
          msg = "xaxis must be different than yaxis"
          raise ProgramError(msg)
  
      return True