def error_perturbation_var(C, S):
    r"""Error-perturbation arising from a given sensitivity

    Parameters
    ----------
    C : (M, M) ndarray
        Count matrix
    S : (K, M, M) ndarray
        Sensitivity tensor

    """
    K = S.shape[0]
    cov = tmatrix_cov(C)
    for i in range(K):
        R = S[i, :, :]
        X[i] = (R[:, :, np.newaxis] * cov * R[:, np.newaxis, :]).sum()