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The ferromagnetic Ising model with zero applied field reduces to sampling even subgraphs X of a graph G with probability proportional to $\lambda^|E(X)|}$, for $\lambda \in [0,1]$. In this paper, we present a class of Markov chains for sampling subgraphs with a fixed set of odd-degree vertices, which generalizes the classical single-site dynamics; when this set is empty, we sample even subgraphs. We use the fact that the set of even subgraphs of a graph $G$ forms a vector space generated by a cycle basis of $G$. In particular, we introduce Markov chains $\m(\C)$ whose transitions are defined by symmetric difference with elements of a cycle basis $\C$. We show that for any graph $G$ and any ''long'' cycle basis $\C$ of $G$, there is a $\lambda$ for which $\m(\C)$ requires exponential time to mix. All fundamental cycle bases of the $d$-dimensional grid are long. For the 2-dimensional grid with periodic boundary conditions we show that there is a $\lambda$ for which $\m(\C)$ requires exponential time to mix for \emphall} bases $\C$.
Streib, N.
and Streib, A.
(2017),
Cycle Basis Markov Chains for the Ising Model, ACM-SIAM Symposium on Discrete Algorithms, Portland, OR, US, [online], https://doi.org/10.1137/1.9781611974775.5, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=914152
(Accessed October 14, 2025)