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Journal of the American Mathematical Society
Journal of the American Mathematical Society
ISSN 1088-6834(online) ISSN 0894-0347(print)

 

Random polynomials with prescribed Newton polytope


Authors: Bernard Shiffman and Steve Zelditch
Journal: J. Amer. Math. Soc. 17 (2004), 49-108
MSC (2000): Primary 12D10, 60D05; Secondary 14Q99, 32H99, 52B20
Published electronically: September 18, 2003
MathSciNet review: 2015330
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Abstract: The Newton polytope $P_f$ of a polynomial $f$ is well known to have a strong impact on its behavior. The Bernstein-Kouchnirenko Theorem asserts that even the number of simultaneous zeros in $(\mathbb{C}^*)^m$ of a system of $m$ polynomials depends on their Newton polytopes. In this article, we show that Newton polytopes also have a strong impact on the distribution of zeros and pointwise norms of polynomials, the basic theme being that Newton polytopes determine allowed and forbidden regions in $(\mathbb{C}^*)^m$ for these distributions.

Our results are statistical and asymptotic in the degree of the polynomials. We equip the space of polynomials of degree $\leq p$ in $m$ complex variables with its usual SU$(m+1)$-invariant Gaussian probability measure and then consider the conditional measure induced on the subspace of polynomials with fixed Newton polytope $P$. We then determine the asymptotics of the conditional expectation $\mathbf{E}_{\vert N P}(Z_{f_1, \dots, f_k})$ of simultaneous zeros of $k$ polynomials with Newton polytope $NP$ as $N \to \infty$. When $P = \Sigma$, the unit simplex, it is clear that the expected zero distributions $\mathbf{E}_{\vert N\Sigma}(Z_{f_1, \dots, f_k})$ are uniform relative to the Fubini-Study form. For a convex polytope $P\subset p\Sigma$, we show that there is an allowed region on which $N^{-k}\mathbf{E}_{\vert N P}(Z_{f_1, \dots, f_k})$ is asymptotically uniform as the scaling factor $N\to\infty$. However, the zeros have an exotic distribution in the complementary forbidden region and when $k = m$ (the case of the Bernstein-Kouchnirenko Theorem), the expected percentage of simultaneous zeros in the forbidden region approaches 0 as $N\to\infty$.


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Additional Information

Bernard Shiffman
Affiliation: Department of Mathematics, Johns Hopkins University, Baltimore, Maryland 21218
Email: shiffman@math.jhu.edu

Steve Zelditch
Affiliation: Department of Mathematics, Johns Hopkins University, Baltimore, Maryland 21218
Email: szelditch@jhu.edu

DOI: http://dx.doi.org/10.1090/S0894-0347-03-00437-5
PII: S 0894-0347(03)00437-5
Keywords: Random polynomial system, distribution of zeros, Newton polytope, Szeg\"o kernel, polytope character, Bernstein-Kouchnirenko Theorem, amoeba, zero current, complex stationary phase
Received by editor(s): March 12, 2002
Received by editor(s) in revised form: May 17, 2003
Published electronically: September 18, 2003
Additional Notes: Research partially supported by NSF grant DMS-0100474 (first author) and DMS-0071358 (second author).
Article copyright: © Copyright 2003 American Mathematical Society