Pólya Positivstellenstaz的度界
Degree bound of Pólya Positivstellenstaz
摘要:
Pólya的Positivstellenbrand上的$1$ -单纯形说,如果$P(x)$是一个真正的多项式,使$P(x)>0$每当$x \ge 0$,然后所有的系数$(1+x)^mP(x)$是积极的,每当$m$是大的。Powers-Reznick对Pólya的Positivstellenstrasse给出了一个复杂度估计。即,他们证明了,对于次数$d$的这种$P(x)$,只要$m > \frac{1}{2} (d^2 -d) \frac{L(P)}{λ(P)} - d$,$(1+x)^mP(x)$的所有系数都是正的。其中$\frac{L(P)}{λ(P)}$是$P(x)$的不变量。对于$d=3$和$d=4$,我们通过显示$d=3$的$m > \frac{3}{2} \frac{L(P)}{λ(P)} - 1$和$d=4$的$ m > \frac{4232}{2505} \frac{L(P)}{λ(P)} - 1$来改进Powers-Reznick结合。
英文摘要:
Pólya's Positivstellensatz on the $1$-simplex says that if $P(x)$ is a real polynomial such that $P(x)>0$ whenever $x \ge 0$, then all the coefficients of $(1+x)^mP(x)$ are positive whenever $m$ is large. Powers-Reznick gave a complexity estimate for Pólya's Positivstellensatz. Namely, they proved that, for such $P(x)$ of degree $d$, all the coefficients of $(1+x)^mP(x)$ are positive whenever $m > \frac{1}{2} (d^2 -d) \frac{L(P)}{λ(P)} - d$. where $\frac{L(P)}{λ(P)}$ is an invariant of $P(x)$. For $d=3$ and $d=4$ specifically, we improve Powers-Reznick's bound by showing $m > \frac{3}{2} \frac{L(P)}{λ(P)} - 1$ for $d=3$ and $ m > \frac{4232}{2505} \frac{L(P)}{λ(P)} - 1$ for $d=4$.
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