Published papers

The Wardrop equilibrium model is widely used for traffic pattern prediction in transportation networks. One of the reasons is that this model can be converted into an equivalent optimization problem, which makes the numerical evaluation of the equilibrium straightforward and efficient. This conversion approach has been extended to networks with link capacities. It is known that the solution of the resulting constrained optimization problem is a flow pattern satisfying an extension of the Wardrop equilibrium. However, the converse does not hold true. We resolve this gap by equilibrium refinement.

© 2019, The Author(s). Consider a monopolistic vendor who faces a known demand curve. By setting a price that equates marginal revenue with marginal cost, the vendor will maximize his profit. This logic holds true of both physical and digital goods. But since digitization will lower the variable production cost, it will strictly increase the profit to the vendor. Then, can we conclude that digitization always improves the vendor’s profitability? Not necessarily. Now consider what will happen on the next day of the sales. Facing deterministic demand, the physical goods vendor must have prepared the exact quantity of the product to sell, and thus all products are sold out. By contrast, the digital goods vendor will have no stock out, thanks to the nature of the digital good. Therefore, the rational vendor will try to sell more and achieve a higher profit after the sales date. To this end, the vendor will now lower the price to attract additional customers with lower reservation prices. The process will indefinitely continue. Knowing this would happen, customers will wait for the price reduction. Even the customers who would have purchased on the first day would defer the purchase until price gets lower. The digital goods vendor will anticipate this and accordingly lower the price on the first day and later, thereby compromising his profitability. Note that this downward spiral takes place as a result of digitization. Thus, digitization may not necessarily improve the profitability to the vendor. We develop an economic model to formally analyze the impact of digitization on the profitability to the vendor.

We investigate how the type of innovation, either of product or process, influences the licensing scheme. For product innovation, we consider a licensing scheme for a patent holder of a new product facing a potential rival who may invest in technology innovation and enter the market for the new product. The alternative forms of licensing schemes considered are fixed fees and royalties. We then compare this licensing scheme for product innovation with that for process innovation studied in the literature.

We consider a game theoretic congestion model with parallel nodes and homogeneous customers. The purpose of this paper is to examine how the priority passes improve social welfare for such a system. To this end, we prove the existence of an equilibrium. The system with no priority pass has a unique equilibrium. With the introduction of priority passes, the uniqueness of the equilibrium may be destroyed. We provide a sufficient condition under which the system with priority passes outperforms the system with no priority passes. The problem is explored numerically as well.

部分的にしか観測できないセミマルコフ過程とそれに関連した多次元リワード過程を動的に解析した。