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arXiv 0903.1287math.OC
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一个凸多项式,它不是sos-凸的

A convex polynomial that is not sos-convex

Amir Ali Ahmadi, Pablo A. Parrilo

摘要:

一个多元多项式$p(x)=p(x_1,...,x_n)$是Sos凸的,如果它的Hessian $H(x)$可以分解为具有可能非平方多项式矩阵$M(x)$的$H(x)= M^T(x) M(x)$。很容易看出,sos-凸性是$p(x)$凸性的充分条件。此外,多项式的自凸性判定问题可以转化为半定规划的可行性问题,从而可以有效地求解。受这种计算上的易处理性的启发,最近有人推测,sos-凸性是否也是多项式凸性的必要条件。在本文中,我们给出了一个明确的例子,三元八次齐次多项式是凸的,但不是sos-凸的否定回答这个问题。有趣的是,我们的例子是使用平方和编程技术和半定优化的对偶理论的软件。作为一个副产品,我们的数值程序,我们得到了一个简单的方法搜索一个有限的家庭的非负多项式,不是平方和。

英文摘要:

A multivariate polynomial $p(x)=p(x_1,...,x_n)$ is sos-convex if its Hessian $H(x)$ can be factored as $H(x)= M^T(x) M(x)$ with a possibly nonsquare polynomial matrix $M(x)$. It is easy to see that sos-convexity is a sufficient condition for convexity of $p(x)$. Moreover, the problem of deciding sos-convexity of a polynomial can be cast as the feasibility of a semidefinite program, which can be solved efficiently. Motivated by this computational tractability, it has been recently speculated whether sos-convexity is also a necessary condition for convexity of polynomials. In this paper, we give a negative answer to this question by presenting an explicit example of a trivariate homogeneous polynomial of degree eight that is convex but not sos-convex. Interestingly, our example is found with software using sum of squares programming techniques and the duality theory of semidefinite optimization. As a byproduct of our numerical procedure, we obtain a simple method for searching over a restricted family of nonnegative polynomials that are not sums of squares.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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