Jian Yang Dept of Computer Science, University College, UNSW, Australian Defence Force Academy, Canberra ACT 2600,
email: jian@csadfa.cs.adfa.oz.au
Wanli Ma
Computer Sciences Laboratory, RSISE,
The Australian National University, Canberra, ACT 0200,
email: ma@discus.anu.edu.au
Richard P. Brent Computer Sciences Laboratory, RSISE, The Australian National University, Canberra, ACT 0200.