docs: def check_args(args):
      """Checks the arguments and options.
  
      :param args: an object containing the options and arguments of the program.
  
      :type args: :py:class:`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 exits with error code 1.
  
      """
      # Checking that the input file exists
      if not os.path.isfile(args.evec):
          m = "{}: no such file".format(args.evec)
          raise ProgramError(m)
      return True