Invited Talks
The following invited talks will be presented on ISSAC 2004
 Numerical Algebraic Geometry and Symbolic Computation
by Jan Verschelde
 Triangulations of Polytopes and Algebraic Geometry
by Francisco Santos
 Sum of Squares of Polynomials and Their Applications
by Pablo Parrilo
In a recent joint work with Andrew Sommese and Charles Wampler,
numerical homotopy continuation methods have been developed to deal
with positive dimensional solution sets of polynomial systems. As
solving polynomial systems is such a fundamental problem, connections
with recent research in symbolic computation are not hard to find. We
will address two such connections.
One part of the numerical output of our methods consists of a
"membership test" used to determine whether a point lies on
a positive dimensional solution component. While Gröbner bases
provide an exact answer to the ideal membership test, geometrical
results can be obtained at a lower complexity, as shown by Giusti and
Heintz. The recent work of Grégoire Lecerf implements an
irreducible decomposition in a symbolic manner.
The factorization of multivariate polynomials with approximate
coefficients was posed as an open problem in symbolic computation by
Erich Kaltofen. Providing a certificate for a numerical factorization
by means of the linear trace is related to ideas of André
Galligo and David Rupprecht, which also appears in the works of
Tateaki Sasaki and collaborators.
The interaction between polyhedral combinatorics and algebraic
geometry is a classical theme. Two examples from the 70's, in which
each discipline has benefited from the other, are the algebraic proof
by Stanley of the Upper Bound Theorem for polytopes and the
BernsteinKouchnirenkoKhovanski Theorem on the number of roots of a
generic sparse system via mixed volumes.
More specifically, triangulations of polytopes and point sets have
algebraicgeometric applications in several contexts. Perhaps the most
celebrated one is the method of Viro for the construction of real
algebraic hypersurfaces with "prescribed" topology. After
reviewing this and other wellknown applications we will discuss in
some more detail the following two recent ones in which the author has
been involved: the construction of nonconnected toric Hilbert schemes
via triangulations of a certain 5dimensional polytope, and the study
of "tropical algebraic geometry" via triangulations of the
product of two simplices.
The existence of a decomposition of a multivariate polynomial as a sum
of squares is a basic question in applied mathematics. It is also one
with important practical consequences, as such decompositions can be
used in the formulation of easily verifiable certificates of the
emptiness of semialgebraic sets. Particularly exciting is the recent
availability of efficient techniques, based on convex optimization,
for its effective computation. In this talk we present an overview of
this novel research area, that combines symbolic and computational
techniques arising from real algebra and numerical optimization.
Along the way, we'll learn how to compute sum of squares
decompositions for polynomials using semidefinite programming, how to
certify the results using rounding techniques, and how to obtain
structured infeasibility certificates for real solutions of systems of
polynomial equations and inequalities. The developed techniques, based
on results from real algebraic geometry, unify and generalize many
wellknown existing methods. The ideas and algorithms will be
illustrated with examples drawn from a broad range of domains,
including geometric theorem proving and quantum mechanics.
