def _get_algorithm(self, algorithm_name):
        """
        Get the specific algorithm.
        :param str algorithm_name: name of the algorithm to use(file name).
        :return: algorithm object.
        """
        try:
            algorithm = anomaly_detector_algorithms[algorithm_name]
            return algorithm
        except KeyError:
            raise exceptions.AlgorithmNotFound('luminol.AnomalyDetector: ' + str(algorithm_name) + ' not found.')