def METHOD_NAME(self):
    """
    returns a tuple of (eigenvalues,eigenvectors) for the data set.
    """
    if self._eig is None:
        res = np.linalg.eig(self.getCovarianceMatrix())
        sorti=np.argsort(res[0])[::-1]
        res=(res[0][sorti],res[1][:,sorti])
        self._eig=res
    return self._eig