Journal of the Operations Research Society of Japan
Online ISSN : 2188-8299
Print ISSN : 0453-4514
ISSN-L : 0453-4514
Volume 66, Issue 1
Displaying 1-5 of 5 articles from this issue
  • Yoshio Matsuyama, Ryota Fujinuma, Yukiya Suzuki, Jin Yoshimura, Yumi A ...
    2023 Volume 66 Issue 1 Pages 1-17
    Published: January 31, 2023
    Released on J-STAGE: February 02, 2023
    JOURNAL FREE ACCESS

    In developing countries, loan sales for expensive products are very common but highly risky because of frequent payment defaults. Because personal credit histories in these countries are imprecise and insufficient compared with those in developed countries, the use of credit scores in loan sales may be very unreliable. Here, to evaluate the reliability of credit scores, we build a simple cost-benefit model of loan management, dividing credit scores into 10 credit score classes (CSCs). As CSC increases, the rough net benefits increase because the total losses caused by payment defaults decrease. The use of credit scores in loan sales is thus found to be highly reliable in developing countries. Combining credit scores with newly developed sources (e.g., mobile phones) may provide highly accurate estimates for loan management.

    Download PDF (318K)
  • Yusuke Kobayashi, Ryoga Mahara
    2023 Volume 66 Issue 1 Pages 18-36
    Published: January 31, 2023
    Released on J-STAGE: February 02, 2023
    JOURNAL FREE ACCESS

    The Steiner tree problem is one of the most fundamental combinatorial optimization problems. In this problem, the input is an undirected graph, a cost function on the edge set, and a subset of vertices called terminals, and the objective is to find a minimum-cost tree spanning all the terminals. By changing the objective function, several variants of the Steiner tree problem have been studied in the literature. For example, in the min-power version of the problem, the goal is to find a Steiner tree S minimizing the total power consumption of vertices, where the power of a vertex v is the maximum cost of any edge of Sincident to v. Another example is the node-weighted version of the problem, in which costs are assigned to vertices instead of edges. In this paper, we introduce a common generalization of these variants and give an approximation algorithm for it. When the maximum degree Δ of the input graph is constant, our algorithm runs in polynomial time and the approximation ratio is 2.016 + ln Δ.

    Download PDF (522K)
  • Pawel Kalczynski, Atsuo Suzuki, Zvi Drezner
    2023 Volume 66 Issue 1 Pages 37-55
    Published: January 31, 2023
    Released on J-STAGE: February 02, 2023
    JOURNAL FREE ACCESS

    The problem considered in this paper is the weighted obnoxious facility location in the convex hull of demand points. The objective function is to maximize the smallest weighted distance between a facility and a set of demand points. Three new global optimal solution approaches are proposed. Two variants of the “Big Triangle Small Triangle” global optimization method, and a procedure based on intersection points between Apollonius circles. We also compared the results with a multi-start approach using the non-linear multi-purpose software SNOPT. Problems with 1,000 demand points are exactly solved in a fraction of a second of computer time.

    Download PDF (721K)
  • Haruki Kamitake, Norio Hibiki
    2023 Volume 66 Issue 1 Pages 56-78
    Published: January 31, 2023
    Released on J-STAGE: February 02, 2023
    JOURNAL FREE ACCESS

    In general, banks keep management costs for card loans down because the amounts are smaller than those of corporate loans. Therefore, they are not sufficiently managed after the money is lent. This study analyzes the deposit and withdrawal data of bank accounts used by card loan borrowers and proposes a default risk management technique. A previous study analyzed bank account data for screening applicants for card loans, and constructed a model to evaluate default risk. However, to the best of our knowledge, there are no studies that analyze bank account data to determine measures for managing the default risk while lending money with a card loan or construct a management model. In addition to the explanatory variables used in the screening model, we employ some variables observable after lending money that are related to individual behavior characteristics, such as number of borrowings and contract repayment rate, and analyze their relationships with default. We construct a logit model using these variables and examine the model using approximately 60 million observations. The result shows that the accuracy ratios exceed 50%, and the model is effective in practice. We also confirm the robustness of the results through cross-validation and an out-of-sample test.

    Download PDF (1345K)
  • Ryutaro Matsumura
    2023 Volume 66 Issue 1 Pages 79-93
    Published: January 31, 2023
    Released on J-STAGE: February 02, 2023
    JOURNAL FREE ACCESS

    This paper proposes a load-balanced algorithm to improve link utilization of inter data center wide area network (IDCWAN) for a backup service. The algorithm obtains more feasible solutions than a heuristic algorithm under heavy demands, and its computation time is acceptable for provisioning IDCWAN. The algorithm belongs to the traffic engineering technology called bandwidth calendaring (BWC), which optimizes the flexible start-of-use time and routing of user demand and can be used for network provisioning. A load-balanced BWC algorithm reduces flows on the busy links during peak time as much as possible. The one-step algorithm is compared with a two-step heuristic one in terms of feasibility and assignment efficiency in numerical experiments, and the former is shown to obtain more feasible solutions than the latter under heavy demands.

    Download PDF (285K)
feedback
Top