Local minima in disordered mean-field ferromagnets

Eric Yilun Song; Reza Gheissari; Charles M. Newman; Daniel L. Stein

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arXiv · 1910.11862

Local minima in disordered mean-field ferromagnets

Eric Yilun Song·Reza Gheissari·Charles M. Newman·Daniel L. Stein

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Abstract

We consider the complexity of random ferromagnetic landscapes on the hypercube $\{\pm 1\}^N$ given by Ising models on the complete graph with i.i.d. non-negative edge-weights. This includes, in particular, the case of Bernoulli disorder corresponding to the Ising model on a dense random graph $\mathcal G(N,p)$. Previous results had shown that, with high probability as $N\to\infty$, the gradient search (energy-lowering) algorithm, initialized uniformly at random, converges to one of the homogeneous global minima (all-plus or all-minus). Here, we devise two modified algorithms tailored to explore the landscape at near-zero magnetizations (where the effect of the ferromagnetic drift is minimized). With these, we numerically verify the landscape complexity of random ferromagnets, finding a diverging number of (1-spin-flip-stable) local minima as $N\to\infty$. We then investigate some of the properties of these local minima (e.g., typical energy and magnetization) and compare to the situation where the edge-weights are drawn from a heavy-tailed distribution.

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Eric Yilun Song, Reza Gheissari, Charles M. Newman, Daniel L. Stein. 2019-10-25. Local minima in disordered mean-field ferromagnets. https://arxiv.org/abs/1910.11862

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