Research Interests

• Mathematical Programming: (1985-Current)

  Prof. Yamada extended the minimum spanning tree problem (MST) to define the mini-max spanning forest problem (MMSF), and developed both of approximate and exact algorithms to solve the problem. In asimilar vein, he also developed algorithms for the knapsack sharingproblem which is an extension of the standard knapsack problem.To solve larger sized problems, meta-heuristic methods such as tabu search, simulated annealing and/orgenetic algorithms are being examined.

• Operations Research: (1972-Current)

  Prof. Yamada has been interested in applying mathematics to solve problems of real life, such as in planning, operations, control and decision making. Broadly speaking, these activities are in the fieldof operations research. His principal research objective in this area has been the application of many OR methods to practical problems. His research in this area includes: city emergency evacuation planning, electoral districting, and class selection problem for collage students.

• Control Systems: (1980-Current)

  Prof. Yamada introduced graph theory to analyze structural propertiesof the so called "descriptor systems", dynamic systems described withdifferential or difference equations with binding static relations.Similar approach have been taken to characterize the "Tinbergen's rule of economy" in terms of the structure of the model. In this regard, controllability of dynamic economic systems can be viewed asan extension of the same rule. A review article in Networks provides a bird's eye view of his research in this area.
  Control of large-scale, complex man-made systems is another research topic of Prof. Yamada. Frequently such a system can be regarded as a discrete event dynamic system, and the Petri net provides a covenient mathematical tool to describe and analyse such a system.He has derived a linear programming formula for the performance evaluation of a subclass of timed Petri nets.