Affiliation: | 1. Department of Computational Mathematics , Kosin University , Pusan, 606-701, Korea E-mail: mailto:jchan@sdg.kosin.ac.kr;2. Department of Mathematics , Okayama University , Okayama, 700, Japan E-mail: mailto:yhirano@math.okayama-u.ac.jp;3. Department of Mathematics , Gyeongsang National University , Jinju, 660-701, Korea E-mail: mailto:hkkim@gshp.gsnu.ac.kr |