## Computing roadmaps of semi-algebraic sets on a variety

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- by Saugata Basu, Richard Pollack and Marie-Françoise Roy
- J. Amer. Math. Soc.
**13**(2000), 55-82 - DOI: https://doi.org/10.1090/S0894-0347-99-00311-2
- Published electronically: July 20, 1999
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## Abstract:

We consider a semi-algebraic set $S$ defined by $s$ polynomials in $k$ variables which is contained in an algebraic variety $Z(Q)$. The variety is assumed to have real dimension $k’,$ the polynomial $Q$ and the polynomials defining $S$ have degree at most $d$. We present an algorithm which constructs a*roadmap*on $S$. The complexity of this algorithm is $s^{k’+1}d^{O(k^2)}$. We also present an algorithm which, given a point of $S$ defined by polynomials of degree at most $\tau$, constructs a path joining this point to the roadmap. The complexity of this algorithm is $k’ s \tau ^{O(1)} d^{O(k^2)}.$ These algorithms easily yield an algorithm which, given two points of $S$ defined by polynomials of degree at most $\tau$, decides whether or not these two points of $S$ lie in the same semi-algebraically connected component of $S$ and if they do computes a semi-algebraic path in $S$ connecting the two points.

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## Bibliographic Information

**Saugata Basu**- Affiliation: Department of Mathematics, University of Michigan, Ann Arbor, Michigan 48109
- MR Author ID: 351826
- Email: saugata@math.lsa.umich.edu
**Richard Pollack**- Affiliation: Courant Institute of Mathematical Sciences, New York University, New York, New York 10012
- Email: pollack@cims.nyu.edu
**Marie-Françoise Roy**- Affiliation: IRMAR (URA CNRS 305), Université de Rennes, Campus de Beaulieu 35042 Rennes cedex, France
- Email: mfroy@univ-rennes1.fr
- Received by editor(s): November 25, 1997
- Received by editor(s) in revised form: April 14, 1999
- Published electronically: July 20, 1999
- Additional Notes: The first author was supported in part by NSF Grants CCR-9402640 and CCR-9424398.

The second author was supported in part by NSF Grants CCR-9402640, CCR-9424398, DMS-9400293, CCR-9711240 and CCR-9732101.

The third author was supported in part by the project ESPRIT-LTR 21024 FRISCO and by European Community contract CHRX-CT94-0506. - © Copyright 1999 American Mathematical Society
- Journal: J. Amer. Math. Soc.
**13**(2000), 55-82 - MSC (1991): Primary 14P10, 68Q25; Secondary 68Q40
- DOI: https://doi.org/10.1090/S0894-0347-99-00311-2
- MathSciNet review: 1685780