1. Mathematical Department, Zhejiang Normal University, Jinhua, 321004, and Mathematical Department, Shaoxing University, Shaoxing, 312000, P.R.C.
2. Mathematical Department, Shaoxing University, Shaoxing, 312004, P.R.C.
3. Centre for Computational Systems Biology, Fudan University, Shanghai, 312000, P.R.C.
4. Centre for Computational Systems Biology, Fudan University, Shanghai, 312000, P.R.C., and Department of Computer Science, Warwick University, Coventry CV4 7AL, U.K.