Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Exact Partition Function for the Potts Model with Next-Nearest Neighbor
  Couplings on Strips of the Square Lattice   We present exact calculations of partition function $Z$ of the $q$-state
Potts model with next-nearest-neighbor spin-spin couplings, both for the
ferromagnetic and antiferromagnetic case, for arbitrary temperature, on
$n$-vertex strip graphs of width $L_y=2$ of the square lattice with free,
cyclic, and M\"obius longitudinal boundary conditions. The free energy is
calculated exactly for the infinite-length limit of these strip graphs and the
thermodynamics is discussed. Considering the full generalization to arbitrary
complex $q$ and temperature, we determine the singular locus ${\cal B}$ in the
corresponding ${\mathbb C}^2$ space, arising as the accumulation set of
partition function zeros as $n \to \infty$.

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The categories of this paper are: supr-con
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The categories of this paper are: astro-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-th
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The categories of this paper are: solv-int
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The categories of this paper are: bayes-an
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The categories of this paper are: cs
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: dg-ga
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The categories of this paper are: cmp-lg
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: stat