arXiv subjects

Shota Fujishima

Publications and source records attributed to Shota Fujishima.

4 recordsLinked to original sources

arXiv2026

Uncovering Functional Blocks in Interregional Production Networks: Evidence from Input-Output Linkages in Japan

This paper examines the latent functional block structure of Japan's production network using interregional input-output data. To isolate non-trivial production linkages, we first estimate a structural gravity model to account for spatial frictions and economic scale, and then apply a weighted stochastic blockmodel (SBM) to the resulting residual network. Because these residual linkages often connect distant regions, the SBM is well suited to grouping region-industry pairs based on their shared macroeconomic roles. The results reveal that even after explicitly filtering out the mechanical effects of geographic proximity, the network is organized into functional blocks that maintain a high degree of regional coherence. Beyond this baseline spatial clustering, we find evidence of cross-regional integration, a structural bifurcation between manufacturing and urban services in metropolitan areas, and broadly spanning primary sectors. These findings provide a network-based perspective on regional coordination, offering guidance for how structurally defined production blocks-rather than simple geographic proximity-can inform wide-area policy design.

physics.soc-ph↗

arXiv2025

From Aggregate Observations to Social Optimum: An Adaptive Pricing Scheme in Heterogeneous Congestion Games

This study investigates an adaptive pricing scheme aimed at achieving an efficient state in a traffic congestion game characterized by a diverse population of road users. While the planner possesses knowledge of players' preferences, their ability to observe only aggregate states limits the implementation of differentiated taxes. We propose a pricing approach that aligns taxes with the true values of externalities over time, ensuring global stability of the social optimum through replicator dynamics. Our findings suggest that the planner, despite being unable to accurately assess externalities at each moment, can still navigate the economy toward a long-term social optimum by adjusting the disaggregated state based on aggregate observations, while acknowledging the challenges posed by heterogeneous value of time (VOT) among drivers. We also find that a pricing mechanism that incorporates the current externalities for each period, which could be executed by a planner with full access to the disaggregated state, might fail to achieve the global stability of the social optimum under the same dynamics.

econ.TH↗

arXiv2023

Identifying sinks and sources of human flows: A new approach to characterizing urban structures

Human flow data are rich behavioral data relevant to people's decision-making regarding where to live, work, go shopping, etc., and provide vital information for identifying city centers. However, it is not as easy to understand massive relational data, and datasets have often been reduced merely to the statistics of trip counts at destinations, discarding relational information from origin to destination. In this study, we propose an alternative center identification method based on human mobility data. This method extracts the scalar potential field of human trips based on combinatorial Hodge theory. It detects not only statistically significant attractive locations as the sinks of human trips but also significant origins as the sources of trips. As a case study, we identify the sinks and sources of commuting and shopping trips in the Tokyo metropolitan area. This aim-specific analysis leads to a combinatorial classification of city centers based on the distinct aspects of human mobility. The proposed method can be applied to other mobility datasets with relevant properties and helps us examine the complex spatial structures in contemporary metropolitan areas from the multiple perspectives of human mobility.

physics.soc-ph↗

arXiv2021

Urban spatial structures from human flow by Hodge-Kodaira decomposition

Human flow in cities indicates social activity and can reveal urban spatial structures based on human behaviours for relevant applications. Scalar potential is a mathematical concept, and if successfully introduced, it can provide an intuitive perspective of human flow. However, the definition of such a potential to the origin-destination flow matrix and determination of its plausibility remain unsolved. Here, we apply Hodge-Kodaira decomposition, in which a matrix is uniquely decomposed into a potential-driven (gradient) flow and a curl flow. We depict the potential landscapes in cities due to commuting flow and reveal how the landscapes have been changed or unchanged by years or transport methods. We then determine how well the commuting flow is described by the potential, by evaluating the percentage of the gradient component for metropolitan areas in the USA and show that the gradient component is almost 100\% in several areas; in other areas, however, the curl component is dominant, indicating the importance of circular flow along triangles of places. The potential landscape provides an easy-to-use visualisation tool to show the attractive places of human flow and will aid in various applications in commerce, urban design, and epidemic spreading.

physics.soc-ph↗