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arXiv · 2302.05813

Lazard-style CAD and Equational Constraints

James H. Davenport·Akshar S. Nair·Gregory K. Sankaran·Ali K. Uncu
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Abstract

McCallum-style Cylindrical Algebra Decomposition (CAD) is a major improvement on the original Collins version, and has had many subsequent advances, notably for total or partial equational constraints. But it suffers from a problem with nullification. The recently-justified Lazard-style CAD does not have this problem. However, transporting the equational constraints work to Lazard-style does reintroduce nullification issues. This paper explains the problem, and the solutions to it, based on the second author's Ph.D. thesis and the Brown--McCallum improvement to Lazard. With a single equational constraint, we can gain the same improvements in Lazard-style as in McCallum-style CAD . Moreover, our approach does not fail where McCallum would due to nullification. Unsurprisingly, it does not achieve the same level of improvement as it does in the non-nullified cases. We also consider the case of multiple equational constraints.

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James H. Davenport, Akshar S. Nair, Gregory K. Sankaran, Ali K. Uncu. 2023-02-11. Lazard-style CAD and Equational Constraints. https://doi.org/10.1145/3597066.3597090

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