Witness computation for solving geometric constraint systems

Arnaud Kubicki, Dominique Michelucci, Sebti Foufou

Research output: Chapter in Book/Report/Conference proceedingConference contribution


In geometric constraint solving, the constraints are represented with an equation system F(U, X) = 0, where X denotes the unknowns and U denotes a set of parameters. The target solution for X is noted XT. A witness is a couple (UW, XW) such that F(UW, XW) = 0. The witness is not the target solution, but they share the same combinatorial features, even when the witness and the target lie on two distinct connected components of the solution set of F(U, X) = 0. Thus a witness enables the qualitative study of the system: the detection of over- and under-constrained systems, the decomposition into irreducible subsystems, the computation of subsystems boundaries. This paper investigates the witness computation in various configurations. The witness computation will be studied under several numerical methods: Newton iterations from random seeds either in R and C, the Broyden-Fletcher-Goldfarb-Shanno method, the Nelder-Mead simplex method. The robustness and performances of these methods will be analyzed and compared. The paper also presents the numerical probabilistic method from which the witness method was originated, and shows how the witness can be used for detecting dependent parameters within systems of geometric constraints.

Original languageEnglish (US)
Title of host publicationProceedings of 2014 Science and Information Conference, SAI 2014
PublisherInstitute of Electrical and Electronics Engineers Inc.
Number of pages12
ISBN (Electronic)9780989319317
StatePublished - Oct 7 2014
Event2014 Science and Information Conference, SAI 2014 - London, United Kingdom
Duration: Aug 27 2014Aug 29 2014

Publication series

NameProceedings of 2014 Science and Information Conference, SAI 2014


Other2014 Science and Information Conference, SAI 2014
Country/TerritoryUnited Kingdom


  • Geometric constraint solving
  • Numerical algorithms
  • Witness computation

ASJC Scopus subject areas

  • Information Systems


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