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Yayoi Abe

Publications and source records attributed to Yayoi Abe.

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Chromatic number of random graphs: an approach using a recurrence relation

The vertex coloring problem to find chromatic numbers is known to be unsolvable in polynomial time. Although various algorithms have been proposed to efficiently compute chromatic numbers, they tend to take an enormous amount of time for large graphs. In this paper, we propose a recurrence relation to rapidly obtain the expected value of the chromatic number of random graphs. Then we compare the results obtained using this recurrence relation with other methods using an exact investigation of all graphs, the Monte Carlo method, the iterated random color matching method, and the method presented in Bollob\'{a}s' previous studies.

math.CO

Cusp singularity in mean field Ising model

An entropy of the Ising model in the mean field approximation is derived by the Hamilton-Jacobi formalism. We consider a grand canonical ensemble with respect to the temperature and the external magnetic field. A cusp arises at the critical point, which shows a simple and new geometrical aspect of this model. In educational sense, this curve with a cusp helps students acquire a more intuitive view on statistical phase transitions.

math-ph