292 research outputs found
Toric Border Bases
We extend the theory and the algorithms of Border Bases to systems of Laurent
polynomial equations, defining "toric" roots. Instead of introducing new
variables and new relations to saturate by the variable inverses, we propose a
more efficient approach which works directly with the variables and their
inverse. We show that the commutation relations and the inversion relations
characterize toric border bases. We explicitly describe the first syzygy module
associated to a toric border basis in terms of these relations. Finally, a new
border basis algorithm for Laurent polynomials is described and a proof of its
termination is given for zero-dimensional toric ideals
A Sparse Flat Extension Theorem for Moment Matrices
In this note we prove a generalization of the flat extension theorem of Curto
and Fialkow for truncated moment matrices. It applies to moment matrices
indexed by an arbitrary set of monomials and its border, assuming that this set
is connected to 1. When formulated in a basis-free setting, this gives an
equivalent result for truncated Hankel operators
Flat extensions in *-algebras
The main result of the paper is a flat extension theorem for positive linear
functionals on *-algebras. The theorem is applied to truncated moment problems
on cylinder sets, on matrices of polynomials and on enveloping algebras of Lie
algebras
Border Basis relaxation for polynomial optimization
A relaxation method based on border basis reduction which improves the
efficiency of Lasserre's approach is proposed to compute the optimum of a
polynomial function on a basic closed semi algebraic set. A new stopping
criterion is given to detect when the relaxation sequence reaches the minimum,
using a sparse flat extension criterion. We also provide a new algorithm to
reconstruct a finite sum of weighted Dirac measures from a truncated sequence
of moments, which can be applied to other sparse reconstruction problems. As an
application, we obtain a new algorithm to compute zero-dimensional minimizer
ideals and the minimizer points or zero-dimensional G-radical ideals.
Experimentations show the impact of this new method on significant benchmarks.Comment: Accepted for publication in Journal of Symbolic Computatio
Exact relaxation for polynomial optimization on semi-algebraic sets
In this paper, we study the problem of computing by relaxation hierarchies
the infimum of a real polynomial function f on a closed basic semialgebraic set
and the points where this infimum is reached, if they exist. We show that when
the infimum is reached, a relaxation hierarchy constructed from the
Karush-Kuhn-Tucker ideal is always exact and that the vanishing ideal of the
KKT minimizer points is generated by the kernel of the associated moment matrix
in that degree, even if this ideal is not zero-dimensional. We also show that
this relaxation allows to detect when there is no KKT minimizer. We prove that
the exactness of the relaxation depends only on the real points which satisfy
these constraints.This exploits representations of positive polynomials as
elementsof the preordering modulo the KKT ideal, which only involves
polynomials in the initial set of variables. Applications to global
optimization, optimization on semialgebraic sets defined by regular sets of
constraints, optimization on finite semialgebraic sets, real radical
computation are given
On the dimension of spline spaces on planar T-meshes
We analyze the space of bivariate functions that are piecewise polynomial of
bi-degree \textless{}= (m, m') and of smoothness r along the interior edges of
a planar T-mesh. We give new combinatorial lower and upper bounds for the
dimension of this space by exploiting homological techniques. We relate this
dimension to the weight of the maximal interior segments of the T-mesh, defined
for an ordering of these maximal interior segments. We show that the lower and
upper bounds coincide, for high enough degrees or for hierarchical T-meshes
which are enough regular. We give a rule of subdivision to construct
hierarchical T-meshes for which these lower and upper bounds coincide. Finally,
we illustrate these results by analyzing spline spaces of small degrees and
smoothness
Isolated points, duality and residues
In this paper, we are interested in the use of duality in effective computations on polynomials. We represent the elements of the dual of the algebra R of polynomials over the field K as formal series in K[[d]] in differential operators. We use the correspondence between ideals of R and vector spaces of K[[d]], stable by derivation and closed for the (d)-adic topology, in order to construct the local inverse system of an isolated point. We propose an algorithm, which computes the orthogonal D of the primary component of this isolated point, by integration of polynomials in the dual space K[d], with good complexity bounds. Then we apply this algorithm to the computation of local residues, the analysis of real branches of a locally complete intersection curve, the computation of resultants of homogeneous polynomials
The Hilbert scheme of points and its link with border basis
In this paper, we give new explicit representations of the Hilbert scheme of
points in \PP^{r} as a projective subvariety of a Grassmanniann
variety. This new explicit description of the Hilbert scheme is simpler than
the previous ones and global. It involves equations of degree . We show how
these equations are deduced from the commutation relations characterizing
border bases. Next, we consider infinitesimal perturbations of an input system
of equations on this Hilbert scheme and describe its tangent space. We propose
an effective criterion to test if it is a flat deformation, that is if the
perturbed system remains on the Hilbert scheme of the initial equations. This
criterion involves in particular formal reduction with respect to border bases
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