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Gram spectrahedra. (English) Zbl 1390.14176
Broglia, Fabrizio (ed.) et al., Ordered algebraic structures and related topics. International conference at CIRM, Luminy, France, October 12–16, 2015. Proceedings. Providence, RI: American Mathematical Society (AMS) (ISBN 978-1-4704-2966-9/pbk; 978-1-4704-4222-4/ebook). Contemporary Mathematics 697, 81-105 (2017).
Summary: Representations of nonnegative polynomials as sums of squares are central to real algebraic geometry and the subject of active research. The sum-of-squares representations of a given polynomial are parametrized by the convex body of positive semidefinite Gram matrices, called the Gram spectrahedron. This is a fundamental object in polynomial optimization and convex algebraic geometry. We summarize results on sums of squares that fit naturally into the context of Gram spectrahedra, present some new results, and highlight related open questions. We discuss sum-of-squares representations of minimal length and relate them to Hermitian Gram spectrahedra and point evaluations on toric varieties.
For the entire collection see [Zbl 1375.00094].

##### MSC:
 14P10 Semialgebraic sets and related spaces
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