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Two-state spin systems with negative interactions

Abstract:
We study the approximability of computing the partition functions of two-state spin systems. The problem is parameterized by a 2 × 2 symmetric matrix. Previous results on this problem were restricted either to the case where the matrix has non-negative entries, or to the case where the diagonal entries are equal, i.e. Ising models. In this paper, we study the generalization to arbitrary 2 × 2 interaction matrices with real entries. We show that in some regions of the parameter space, it’s #P-hard to even determine the sign of the partition function, while in other regions there are fully polynomial approximation schemes for the partition function. Our results reveal several new computational phase transitions.
Publication status:
In press
Peer review status:
Peer reviewed

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Publisher copy:
10.1016/j.ic.2025.105340

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Institution:
University of Oxford
Division:
MPLS
Department:
Computer Science
Role:
Author
ORCID:
0000-0003-1879-6089


Publisher:
Elsevier
Journal:
Information and Computation More from this journal
Publication date:
2025-08-25
Acceptance date:
2025-08-14
DOI:
EISSN:
1090-2651
ISSN:
0890-5401


Language:
English
Pubs id:
2281457
Local pid:
pubs:2281457
Deposit date:
2025-08-15

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