Abstract
We present an optimal version of Descartes’ rule of signs to bound the number of positive real roots of a sparse system of polynomial equations in n variables with \(n+2\) monomials. This sharp upper bound is given in terms of the sign variation of a sequence associated to the exponents and the coefficients of the system.
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Acknowledgements
We are grateful to the referee for several interesting comments; in particular, for pointing out that inequality (20) could be interpreted as a discrete version of Rolle’s theorem on \(\mathbb {R}/k \mathbb {Z}\).
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Communicated by Jean-Yves Welschinger.
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AD was partially supported by UBACYT 20020100100242, CONICET PIP 20110100580, and ANPCyT PICT 2013-1110, Argentina. FB was partially supported by grant ANR-18-CE40-0009 “ENUMGEOM” of Agence Nationale de Recherche. JF was funded by SNSF grant #159240 “Topics in tropical and real geometry,” the NCCR SwissMAP project, and NWO-grant TOP1EW.15.313.
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Bihan, F., Dickenstein, A. & Forsgård, J. Optimal Descartes’ rule of signs for systems supported on circuits. Math. Ann. 381, 1283–1307 (2021). https://doi.org/10.1007/s00208-021-02216-4
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DOI: https://doi.org/10.1007/s00208-021-02216-4