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Speaker:
D. Grigoriev
Date:
Thu, 15/01/2015 - 15:00 - 16:00
Location:
MPIM Lecture Hall
Parent event:
MPI-Oberseminar We show that bounds in tropical geometry can have for some problems features of complex geometry and for other problems of real geometry. We prove (jointly with V. Podolskii) a tropical dual effective Nullstellensatz which states that a system of tropical polynomials $f_1,\dots, f_k$ in $n$ variables of degrees $d_1\ge \cdots \ge d_k$ has a solution iff a finite (truncated) submatrix of (infinite) Macauley matrix of the system has a tropical solution. The size of truncation depends on the sum of degrees $d_1+\cdots + d_k$ in case of a tropical semi-ring without infinity. In case of a tropical semi-ring with infinity the size of truncation depends on the product of degrees $d_1 \cdots d_n$ (Bezout number). The bounds are close to sharp. This phenomenon resembles the classical effective Nullstellensatz in the complex geometry for which a similar bound being the sum of degrees holds in the projective case (Macauley-Lazard), while the bound being the product of degrees emerges in the affine case (Brownawell-Galligo-Giusti-Heintz-Kollar). We consider the dual Nullstellensatz since the classical Hilbert's one fails in the tropical world. On the other hand, the sum of Betti numbers of a tropical prevariety given by $f_1,\dots, f_k$ is less than by ${k+n \choose n} \cdot d_1\cdots d_n$ (a joint result with A. Davydow), which resembles Oleinik-Petrovsky-Milnor-Thom bound on the sum of Betti numbers of a real semi-algebraic set. Again, this bound is close to sharp.
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