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34
An Explicit Construction of Distinguished Representations of Polynomials Nonnegative Over Finite Sets
, 2002
"... We present a simple constructive proof of the existence of distinguished sum of squares representations for polynomials nonnegative over finite sets described by polynomial equalities and inequalities. A degree bound is directly obtained, as the cardinality of the support of the summands equals t ..."
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Cited by 23 (4 self)
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We present a simple constructive proof of the existence of distinguished sum of squares representations for polynomials nonnegative over finite sets described by polynomial equalities and inequalities. A degree bound is directly obtained, as the cardinality of the support of the summands equals the number of points in the variety. Only basic results from commutative algebra are used in the construction.
Verifying nonlinear real formulas via sums of squares
 Theorem Proving in Higher Order Logics, TPHOLs 2007, volume 4732 of Lect. Notes in Comp. Sci
, 2007
"... Abstract. Techniques based on sums of squares appear promising as a general approach to the universal theory of reals with addition and multiplication, i.e. verifying Boolean combinations of equations and inequalities. A particularly attractive feature is that suitable ‘sum of squares ’ certificates ..."
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Cited by 19 (2 self)
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Abstract. Techniques based on sums of squares appear promising as a general approach to the universal theory of reals with addition and multiplication, i.e. verifying Boolean combinations of equations and inequalities. A particularly attractive feature is that suitable ‘sum of squares ’ certificates can be found by sophisticated numerical methods such as semidefinite programming, yet the actual verification of the resulting proof is straightforward even in a highly foundational theorem prover. We will describe our experience with an implementation in HOL Light, noting some successes as well as difficulties. We also describe a new approach to the univariate case that can handle some otherwise difficult examples. 1 Verifying nonlinear formulas over the reals Over the real numbers, there are algorithms that can in principle perform quantifier elimination from arbitrary firstorder formulas built up using addition, multiplication and the usual equality and inequality predicates. A classic example of such a quantifier elimination equivalence is the criterion for a quadratic equation to have a real root: ∀a b c. (∃x. ax 2 + bx + c = 0) ⇔ a = 0 ∧ (b = 0 ⇒ c = 0) ∨ a � = 0 ∧ b 2 ≥ 4ac
Positive polynomials in scalar and matrix variables, the spectral theorem, and optimization
 , in vol. Structured Matrices and Dilations. A Volume Dedicated to the Memory of Tiberiu Constantinescu
"... We follow a stream of the history of positive matrices and positive functionals, as applied to algebraic sums of squares decompositions, with emphasis on the interaction between classical moment problems, function theory of one or several complex variables and modern operator theory. The second par ..."
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Cited by 13 (3 self)
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We follow a stream of the history of positive matrices and positive functionals, as applied to algebraic sums of squares decompositions, with emphasis on the interaction between classical moment problems, function theory of one or several complex variables and modern operator theory. The second part of the survey focuses on recently discovered connections between real algebraic geometry and optimization as well as polynomials in matrix variables and some control theory problems. These new applications have prompted a series of recent studies devoted to the structure of positivity and convexity in a free ∗algebra, the appropriate setting for analyzing inequalities on polynomials having matrix variables. We sketch some of these developments, add to them and comment on the rapidly growing literature.
On the Equivalence of Algebraic Approaches to the Minimization of Forms on the Simplex
, 2003
"... We consider the problem of minimizing a form on the standard simplex [equivalently, the problem of minimizing an even form on the unit sphere]. Converging hierarchies of approximations for this problem can be constructed, that are based, respectively, on results by SchmudgenPutinar and by Polya ..."
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Cited by 9 (5 self)
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We consider the problem of minimizing a form on the standard simplex [equivalently, the problem of minimizing an even form on the unit sphere]. Converging hierarchies of approximations for this problem can be constructed, that are based, respectively, on results by SchmudgenPutinar and by Polya about representations of positive polynomials in terms of sums of squares. We show that the two approaches yield, in fact, the same approximations. The same type of argument also permits to establish some representation results a la Polya for positive polynomials on semialgebraic cones.
LMI approximations for cones of positive semidefinite forms
 Fachbereich Mathematik, Universität Konstanz, 78457
"... An interesting recent trend in optimization is the application of semidefinite programming techniques to new classes of optimization problems. In particular, this trend has been successful in showing that under suitable circumstances, polynomial optimization problems can be approximated via a sequen ..."
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Cited by 8 (2 self)
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An interesting recent trend in optimization is the application of semidefinite programming techniques to new classes of optimization problems. In particular, this trend has been successful in showing that under suitable circumstances, polynomial optimization problems can be approximated via a sequence of semidefinite programs. Similar ideas apply to conic optimization over the cone of copositive matrices, and to certain optimization problems involving random variables with some known moment information. We bring together several of these approximation results by studying the approximability of cones of positive semidefinite forms (homogeneous polynomials). Our approach enables us to extend the existing methodology to new approximation schemes. In particular, we derive a novel approximation to the cone of copositive forms, that is, the cone of forms that are positive semidefinite over the nonnegative orthant. The format of our construction can be extended to forms that are positive semidefinite over more general conic domains. We also construct polyhedral approximations to cones of positive semidefinite forms over a polyhedral domain. This opens the possibility of using linear programming technology in optimization problems over these cones.
Representation of real commutative rings
 Expo. Math
, 2005
"... During the last 10 years there have been several results on the representation of real polynomials, positive on some semialgebraic subset of R n. These results started with a solution of the moment problem by Schmüdgen for corresponding sets. Later Wörmann realized that the same results could be ob ..."
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Cited by 5 (0 self)
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During the last 10 years there have been several results on the representation of real polynomials, positive on some semialgebraic subset of R n. These results started with a solution of the moment problem by Schmüdgen for corresponding sets. Later Wörmann realized that the same results could be obtained by the socalled “KadisonDubois ” Representation Theorem. The aim of our talk is to present this representation theorem together with its history, and to discuss its implication to the representation of positive polynomials. Also recent improvements of both topics by T. Jacobi and the author will be included. 1 The real representation theorem. Roughly speaking, the purpose of a representation theorem is, to start with awellknown mathematical structure, generalize (axiomatize) it and try to ‘represent ’ the generalized structures in terms of the old one. In our case, the ring that is assumed to be wellknown is the ring C(X, R) of continuous realvalued functions on a compact hausdorff space X. This ring carries a natural partial order given by Thus the set f ≤ g iff f(x) ≤ g(x) for all x ∈ X. T0 = {f ∈ C(X, R)  f ≥ 0onX} is a preordering of the ring C = C(X, R), i.e., we have
Closures of Quadratic Modules
 2 CLOSED SEPARATION THEOREMS 19
"... Abstract. We consider the problem of determining the closure M of a quadratic module M in a commutative Ralgebra with respect to the finest locally convex topology. This is of interest in deciding when the moment problem is solvable [26] [27] and in analyzing algorithms for polynomial optimization ..."
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Cited by 5 (4 self)
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Abstract. We consider the problem of determining the closure M of a quadratic module M in a commutative Ralgebra with respect to the finest locally convex topology. This is of interest in deciding when the moment problem is solvable [26] [27] and in analyzing algorithms for polynomial optimization involving semidefinite programming [12]. The closure of a semiordering is also considered, and it is shown that the space YM consisting of all semiorderings lying over M plays an important role in understanding the closure of M. The result of Schmüdgen for preorderings in [27] is strengthened and extended to quadratic modules. The extended result is used to construct an example of a nonarchimedean quadratic module describing a compact semialgebraic set that has the strong moment property. The same result is used to obtain a recursive description of M which is valid in many cases. In Section 1 we consider the general relationship between the closure C and the sequential closure C ‡ of a subset C of a real vector space V in the finest locally convex topology. We are mainly interested in the case where C is a cone in V. We consider cones with nonempty interior and cones satisfying C ∪ −C = V. In Section 2 we begin our investigation of the closure M of a quadratic module M of a commutative Ralgebra A; the focus is on finitely generated quadratic modules in finitely generated algebras. The closure of a semiordering Q of A is also considered, and it is shown that the space YM consisting of all semiorderings of A lying over M plays an important role in understanding the closure of M; see Propositions 2.2, 2.3 and 2.4. The result of Schmüdgen for preorderings in [27] is strengthened and extended to quadratic modules; see Theorem 2.8. In Section 3 we consider the case of quadratic modules that describe compact semialgebraic sets. We use Theorem 2.8 to deduce various results; see Theorems 3.1 and 3.4; and also to construct an example where KM is compact, M satisfies the strong moment property (SMP), but M is not archimedean; see Example 3.7.
A general representation theorem for partially ordered commutative rings
"... Abstract. An extension of the KadisonDubois representation theorem is proved. This extends both the classical version [3] and the preordering version given by Jacobi in [5]. It is then shown how this can be used to sharpen the results on representations of strictly positive polynomials given by Jac ..."
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Cited by 5 (3 self)
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Abstract. An extension of the KadisonDubois representation theorem is proved. This extends both the classical version [3] and the preordering version given by Jacobi in [5]. It is then shown how this can be used to sharpen the results on representations of strictly positive polynomials given by Jacobi and Prestel in [6]. In [4] Dubois extends a result of Kadison on representation of archimedean partially ordered Banach algebras [7] to a more general class of rings called Stone rings. This is the socalled KadisonDubois theorem. 1 It is used in real algebra, e.g., by Becker [2], in his study of sums of 2nth powers and the real holomorphy ring of a field. In [3] Becker and Schwartz give a short elementary proof in the commutative case. In his solution of the moment problem in [13], Schmüdgen gives a representation of polynomials strictly positive on a bounded basic closed semialgebraic set in Rn.Putinar [12] gives a criterion for ‘linear ’ representations to exist. Jacobi and Prestel [6] show how Schmüdgen’s representation can be improved and determine exactly when the linear representations considered by Putinar are possible. Schmüdgen and Putinar use methods from functional analysis. In [14] Wörmann uses the KadisonDubois theorem to give a purely algebraic proof of Schmüdgen’s result. In [5] Jacobi proves a new variant of the KadisonDubois theorem and uses this to give an algebraic proof of Putinar’s criterion for linear representations. In the present paper we prove a general representation theorem for archimedean Tmodules, T a weakly torsion preprime; see Theorem 2.3. This extends both the classical KadisonDubois theorem in [3] and the version given by Jacobi in [5]. In Section 3 it is explained how this can be used to sharpen the results on representations of strictly positive polynomials given in [6]; also see [10, Sect. 5.4].
The convex Positivstellensatz in a free algebra
 Adv. Math
"... Abstract. The main result of this paper establishes the perfect noncommutative Nichtnegativstellensatz on a convex semialgebraic set: suppose L is a monic linear pencil in g variables and let DL be its positivity domain DL: = ⋃ {} n×n g ..."
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Cited by 4 (3 self)
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Abstract. The main result of this paper establishes the perfect noncommutative Nichtnegativstellensatz on a convex semialgebraic set: suppose L is a monic linear pencil in g variables and let DL be its positivity domain DL: = ⋃ {} n×n g
Infeasibility certificates for linear matrix inequalities
"... Abstract. Farkas ’ lemma is a fundamental result from linear programming providing linear certificates for infeasibility of systems of linear inequalities. In semidefinite programming, such linear certificates only exist for strongly infeasible linear matrix inequalities. We provide nonlinear algebr ..."
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Cited by 3 (1 self)
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Abstract. Farkas ’ lemma is a fundamental result from linear programming providing linear certificates for infeasibility of systems of linear inequalities. In semidefinite programming, such linear certificates only exist for strongly infeasible linear matrix inequalities. We provide nonlinear algebraic certificates for all infeasible linear matrix inequalities in the spirit of real algebraic geometry. More precisely, we show that a linear matrix inequality L(x) ≽ 0 is infeasible if and only if −1 lies in the quadratic module associated to L. We prove exponential degree bounds for the corresponding algebraic certificate. In order to get a polynomial size certificate, we use a more involved algebraic certificate motivated by the real radical and Prestel’s theory of semiorderings. Completely different methods, namely complete positivity from operator algebras, are employed to consider linear matrix inequality domination. A linear matrix inequality (LMI) is a condition of the form n∑ L(x) = A0 + xiAi ≽ 0 (x ∈ R n)