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arXiv · 2204.07236

A* shortest string decoding for non-idempotent semirings

Kyle Gorman·Cyril Allauzen
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Abstract

The single shortest path algorithm is undefined for weighted finite-state automata over non-idempotent semirings because such semirings do not guarantee the existence of a shortest path. However, in non-idempotent semirings admitting an order satisfying a monotonicity condition (such as the plus-times or log semirings), the notion of shortest string is well-defined. We describe an algorithm which finds the shortest string for a weighted non-deterministic automaton over such semirings using the backwards shortest distance of an equivalent deterministic automaton (DFA) as a heuristic for A* search performed over a companion idempotent semiring, which is proven to return the shortest string. While there may be exponentially more states in the DFA, this algorithm needs to visit only a small fraction of them if determinization is performed "on the fly".

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Kyle Gorman, Cyril Allauzen. 2022-04-14. A* shortest string decoding for non-idempotent semirings. https://arxiv.org/abs/2204.07236

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