[1
]School of Information Science and Engineering; Chengdu University; Chengdu 610106
P.R. China
[2
]Department of Computer and Information Science; University of Macau; Macau P.R. China
[3
]Department of Applied Mathematics; University of Waterloo; Waterloo Ontario Canada
[4
]School of Mathematical Sciences; University of Electronic Science and Technology of
China; Chengdu 611731 P.R. China