arXiv subjects

Victoria Powers

Publications and source records attributed to Victoria Powers.

6 recordsLinked to original sources

arXiv2019

A note on mediated simplices

Many homogeneous polynomials that arise in the study of sums of squares and Hilbert's 17th problem come from monomial substitutions into the arithmetic-geometric inequality. In 1989, the second author gave a necessary and sufficient condition for such a form to have a representation as a sum of squares of forms (Math. Ann., (283), 431--464), involving the arrangement of lattice points in the simplex whose vertices were the $n$-tuples of the exponents used in the substitution. Further, a claim was made, and not proven, that sufficiently large dilations of any such simplex will also satisfy this condition. The aim of this short note is to prove the claim, and provide further context for the result, both in the study of Hilbert's 17th Problem and the study of lattice point simplices.

math.CO↗

arXiv2019

Power index rankings in bicameral legislatures and the US legislative system

In this paper we study rankings induced by power indices of players in simple game models of bicameral legislatures. For a bicameral legislature where bills are passed with a simple majority vote in each house we give a condition involving the size of each chamber which guarantees that a member of the smaller house has more power than a member of the larger house, regardless of the power index used. The only case for which this does not apply is when the smaller house has an odd number of players, the larger house has an even number of players, and the larger house is less than twice the size of the smaller house. We explore what can happen in this exceptional case. These results generalize to multi-cameral legislatures. Using a standard model of the US legislative system as a simple game, we use our results to study power index rankings of the four types of players -- the president, the vice president, senators, and representatives. We prove that a senator is always ranked above a representative and ranked the same as or above the vice president. We also show that the president is always ranked above the other players. We show that for most power index rankings, including the Banzhaf and Shapley-Shubik power indices, the vice president is ranked above a representative, however, there exist power indices ranking a representative above the vice president.

math.CO↗

arXiv2010

Polynomials non-negative on strips and half-strips

In 2008, M. Marshall settled a long-standing open problem by showing that if f(x,y) is a polynomial that is non-negative on the strip [0,1] x R, then there exist sums of squares s(x,y) and t(x,y) such that f(x,y) = s(x,y) + (x - x^2) t(x,y). In this paper, we generalize Marshall's result to various strips and half-strips in the plane. Our results give many new examples of non-compact semialgebraic sets in R^2 for which one can characterize all polynomials which are non-negative on the set. For example, we show that if U is a compact set in the real line and {g_1, ..., g_k} a specific set of generators for U as a semialgebraic set, then whenever f(x,y) is non-negative on U x R, there are sums of squares s_0, ..., s_k such that f = s_0 + s_1 g_1 + ... + s_k g_k.

math.AG↗

arXiv2009

Rational certificates of positivity on compact semialgebraic sets

Schmüdgen's Theorem says that if a basic closed semialgebraic set K = {g_1 \geq 0, ..., g_s \geq 0} in R^n is compact, then any polynomial f which is strictly positive on K is in the preordering generated by the g_i's. Putinar's Theorem says that under a condition stronger than compactness, any f which is strictly positive on K is in the quadratic module generated by the g_i's. In this note we show that if the g_i's and the f have rational coefficients, then there is a representation of f in the preordering with sums of squares of polynomials over Q. We show that the same is true for Putinar's Theorem as long as we include among the generators a polynomial N - \sum X_i^2, N a natural number.

math.AG↗

arXiv2005

Minimizing Polynomials Over Semialgebraic Sets

This paper concerns a method for finding the minimum of a polynomial on a semialgebraic set, i.e., a set in $\re^m$ defined by finitely many polynomial equations and inequalities, using the Karush-Kuhn-Tucker (KKT) system and sum of squares (SOS) relaxations. This generalizes results in the recent paper \cite{njw_grad}, which considers minimizing polynomials on algebraic sets, i.e., sets in $\re^m$ defined by finitely many polynomial equations. Most of the theorems and conclusions in \cite{njw_grad} generalize to semialgebraic sets, even in the case where the semialgebraic set is not compact. We discuss the method in some special cases, namely, when the semialgebraic set is contained in the nonnegative orthant $\re^n_+$ or in box constraints $[a,b]_n$. These constraints make the computations more efficient.

math.OC↗

arXiv2004

A New Proof of Hilbert's Theorem on Ternary Quartics

David Hilbert proved that a non-negative real quartic form f(x,y,z) is the sum of three squares of quadratic forms. We give a new proof which shows that if the complex plane curve Q defined by f is smooth, then f has exactly 8 such representations, up to equivalence. They correspond to those real 2-torsion points of the Jacobian of Q which are not represented by a conjugation-invariant divisor on Q.

math.AG↗