1COLLEGE OF HUMANITIES AND Sciences, NIHON UNIVERSITY, 3-25-40 SAKURAJOSUI SETAGAYA- KU Tokyo 156-8550, JAPAN
2GRrapH THEORY AND APPLICATIONS RESEARCH GROUP, SCHOOL OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCE, FACULTY OF ENGINEERING AND BUILT ENVIRONMENT, THE UNIVERSITY orf NEwcasTLe, NSW 2308 AUSTRALIA