1. Univ. Rennes, CNRS, INRIA-MINGuS, IRMAR-UMR 6625, F-35000 Rennes, France
2. School of Mathematics and Statistics & Hubei Key Laboratory of Computational Science, Wuhan University, Wuhan, 430072, China; Univ. Rennes, INRIA-MINGuS, CNRS, IRMAR-UMR 6625, F-35000 Rennes, France