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A New SAT Encoding of the At- Most-One Constraint Jingchao Chen Donghua University, China

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2 Definition At-Most-One (AMO) constraint: Given X = {x 1,x 2,…,x n } of n Boolean variables, at most one out of n variables in X is allowed to be true. AMO encoding: Convert AMO constraint to SAT problem in CNF

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3 Known AMO encodings standard AMO encoding: AMO(X)={ x i ∨ x j | x i, x j ∈ X,i

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4 A summary of AMO encodings Methodinventorclausesaux. vars standardfolkloren*(n-1)/20 bitwiseFrisch et al.n log nlog n sequentialSinz3n-4n-1 2-productThis paper

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5 Basic Idea of a Product Encoding u 1 u 2 · · · · · · · · · · · · ·u i · · · · · · u p vqvjv2v1vqvjv2v1 x 1 x 2 · · · · · · · · · · · · · · · · · · · · ·x p x p+1 x p+2 · · · · · · · · · · · · · · · ·· ·x 2p x jp-p+1 x jp-p+2 · · · · · · · · x k · · · · x jp x qp-p+1 x qp-p+2 · · · · · · · · · · · · · x pq n≈pq x k →

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6 Example n=5, p=3, q=2 v2v1v2v1 u 1 u 2 u 3 x 1 x 2 x 3 x 4 x 5

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7 Basic formula of 2-product encoding where X={x 1,x 2,…x n }, U={u 1,u 2,…u p }, V={v 1,v 2,…v q }

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8 Property (1) of 2-product encoding If using the sequential encoding to encode sub-constraints AMO (U) and AMO (V), the 2-product encoding requires 2n + 3p-4 +3q-4 ≈ clauses and auxiliary variables.

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9 Property (2) of 2-product encoding If using the standard encoding to encode sub-constraints AMO (U) and AMO (V), the 2-product encoding requires 2n + p(p-1)/2 + q(q-1)/2 ≈ clauses and auxiliary variables.

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10 Property (3) of 2-product encoding If encoding sub-constraints AMO (U) and AMO (V) in a recursive way, the 2-product encoding requires clauses and auxiliary variables.

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11 k-product encoding map(X,W 1,W 2,…W k ) denotes each point in X is defined by a point in W 1 ×W 2 ×…×W k. It consists of the following clauses. |W 1 |=|W 2 |=…=|W k |=p

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12 Property of k-product encoding When |W 1 |=|W 2 |=…=|W k |=p=2, k-product encoding become a bitwise encoding. If using the standard encoding to encode sub- constraints AMO(W i ), |W i |=p=, the k-product encoding of AMO requires clauses and auxiliary variables.

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13 Empirical evaluation Table 1. The number of clauses and auxiliary variables required to encode AMO constraints of edge-matching problems.

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14 Table 2. Runtime (in seconds) required by CircleSAT to solve edge-matching problems based on various AMO encodings.

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15 Conclusions Present four versions of the product AMO encoding 2-product encoding requires the minimal clauses Unit propagation on product encoding achieves arc- consistency.

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16 Thank you

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