# A note on the complexity of univariate root isolation

2 GEOMETRICA - Geometric computing
CRISAM - Inria Sophia Antipolis - Méditerranée
Abstract : This paper presents the average-case bit complexity of subdivision-based univariate solvers, namely those named after Sturm, Descartes, and Bernstein. By real solving we mean real root isolation. We prove bounds of $\sOB(N^5)$ for all methods, where $N$ bounds the polynomial degree and the coefficient bitsize, whereas their worst-case complexity is in $\sOB(N^6)$. In the case of the Sturm solver, our bound depends on the number of real roots. Our work is a step towards understanding the practical complexity of real root isolation. This enables a better juxtaposition against numerical solvers, the latter having worst-case complexity in $\sOB(N^4)$. % Our approach extends to complex root isolation, where we offer a simple proof leading to bounds % for the number of steps that the subdivision algorithm performs on the worst and average-case complexities of $\sOB(N^7 )$ and $\sOB(N^6)$ respectively, where the latter is output-sensitive.
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Reports

Cited literature [34 references]

https://hal.inria.fr/inria-00116985
Contributor : Elias Tsigaridas <>
Submitted on : Sunday, December 10, 2006 - 6:05:28 PM
Last modification on : Thursday, November 26, 2020 - 4:00:02 PM
Long-term archiving on: : Friday, September 24, 2010 - 11:58:11 AM

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RR-6043.pdf
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• HAL Id : inria-00116985, version 5

### Citation

Ioannis Emiris, Elias P. Tsigaridas. A note on the complexity of univariate root isolation. [Research Report] RR-6043, INRIA. 2006, pp.18. ⟨inria-00116985v5⟩

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