“Towards a multidimensional Descartes rule (but still far away)”
The classical Descartes’ rule of signs bounds the number of positive real roots of a univariate real polynomial in terms of the number of sign variations of its coe_cients. This is an extremely simple rule which is exact when all the roots are real, for instance, for characteristic polynomials of symmetric matrices. No general multivariate generalization is known for this rule, not even a conjectural one.
Prof. Dickenstein will gently describe two partial multivariate generalizations obtained in collaboration with Stefan Müller, Elisenda Feliu, Georg Regensburger, Anne Shiu, Carsten Conradi, Frédéric Bihan and Jens Forsgaard. This approach shows that the number of positive roots of a square polynomial system (of n polynomials in n variables) is related to the signs of the maximal minors of the matrix of exponents and of the matrix of coe_cients. She will also explain which are the main challenges to devise a complete multivariate generalization.