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arXiv 0708.3522math.AGcs.SCmath.ATmath.GT
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由部分二次多项式组定义的半代数集的贝蒂数的界及Euler-Poincaré特征的计算

Bounding the Betti numbers and computing the Euler-Poincaré characteristic of semi-algebraic sets defined by partly quadratic systems of polynomials

Saugata Basu, Dmitrii V. Pasechnik, Marie-Francoise Roy

摘要:

设$\R$是实闭域,$ {\mathcal Q} \subset \R[Y_1,...,Y_\ell,X_1,...,X_k], $有$ °_{Y}(Q) \leq 2, °_{X}(Q) \leq d, Q \in {\mathcal Q}, #({\mathcal Q})=m,$,$ {\mathcal P} \subset \R[X_1,...,X_k] $有$°_{X}(P) \leq d, P \in {\mathcal P}, #({\mathcal P})=s$,$S \subset \R^{\ell+k}$是由布尔公式定义的半代数集,无否定,有原子$P=0, P \geq 0, P \leq 0, P \in {\mathcal P} \cup {\mathcal Q}$ .证明了$S$的贝蒂数之和是由\[ \ell^2 (O(s+\ell+m)\ell d)^{k+2m}. \]有界的。这是以前关于分别由$d$和2次多项式定义的闭半代数集的贝蒂数的有界结果的一般推广。我们还描述了一个算法,用于计算欧拉-庞加莱特性的这样的集合,推广类似的算法之前已知的。该算法的复杂度以$(\ell s m d)^{O(m(m+k))}$为界。

英文摘要:

Let $\R$ be a real closed field, $ {\mathcal Q} \subset \R[Y_1,...,Y_\ell,X_1,...,X_k], $ with $ °_{Y}(Q) \leq 2, °_{X}(Q) \leq d, Q \in {\mathcal Q}, #({\mathcal Q})=m,$ and $ {\mathcal P} \subset \R[X_1,...,X_k] $ with $°_{X}(P) \leq d, P \in {\mathcal P}, #({\mathcal P})=s$, and $S \subset \R^{\ell+k}$ a semi-algebraic set defined by a Boolean formula without negations, with atoms $P=0, P \geq 0, P \leq 0, P \in {\mathcal P} \cup {\mathcal Q}$. We prove that the sum of the Betti numbers of $S$ is bounded by \[ \ell^2 (O(s+\ell+m)\ell d)^{k+2m}. \] This is a common generalization of previous results on bounding the Betti numbers of closed semi-algebraic sets defined by polynomials of degree $d$ and 2, respectively. We also describe an algorithm for computing the Euler-Poincaré characteristic of such sets, generalizing similar algorithms known before. The complexity of the algorithm is bounded by $(\ell s m d)^{O(m(m+k))}$.

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