1. Department of Applied Mathematics Science, Faculty of Science Tokyo University of Science 1‐3 Kagurazaka, Shinjuku‐ku Tokyo 162‐8601Japan
2. Research School of Finance, Actuarial Studies & Statistics Australian National University Acton ACT 2601Australia
3. Department of Applied Mathematics Science, Graduate School of Science Tokyo University of Science Shinjuku‐ku Tokyo 162‐8601Japan
4. Center for Educational Outreach and Admissions Kyoto University 606‐8501Kyoto Japan