def METHOD_NAME(self):
    gf_struct = [('up',2), ('dn',2)]
    U, V = 1., 1.
    h_int = U * (n('up',0) * n('dn',0) + n('up',1) * n('dn',1)) + \
            V * (n('up',0) * n('dn',1) + n('up',1) * n('dn',0))
    U_dict2 = extract_U_dict2(h_int)
    print(U_dict2)
    print(dict_to_matrix(U_dict2, gf_struct))