Authors:
Juan F. Camino,
J. William Helton,
Robert E. Skelton,
Volume: 1, Page 5023 Paper number 1776
Abstract:
Inequalities involving polynomials in matrices and their inverses and
associated optimization problems have become very important in engineering.
When these polynomials are ``matrix convex'' interior point methods
apply directly. A difficulty is that often an engineering problem
presents a matrix polynomial problem whose convexity takes considerable
skill, time, and luck to determine. Typically this is done by looking
at a formula and recognizing complicated patterns involving Schur complements;
a tricky hit or miss procedure. Certainly computer assistance in determining
convexity would be valuable. This paper describes some symbolic methods
and software which represent a beginning along these lines. Our procedure
proceeds automatically and completely avoids Schur complement wizardry.
[New Paragraph] The paper presents an algorithm which takes in a noncommutative
rational function F(X,Y) of X,Y and puts out a family of inequalities
which determine a domain G of X and Y on which F is ``matrix convex''.
Somewhat surprising and decidedly non-trivial is our main theorem showing
that when the variable X is symmetric the domain G determined by our
algorithm is, in a certain sense, the ``largest'' possible domain of
matrix convexity for G. [New Paragraph] Of possible independent interest
in this article is a theory of positivity of noncommutative quadratic
functions and a noncommutative LDU algorithm. The algorithms described
here have been implemented under Mathematica and the noncommutative
algebra package NCAlgebra. They are available at www.math.ucsd.edu/~ncalg.
Examples presented in this article illustrate some of this software.
Authors:
Scott A. Miller,
Roy S. Smith,
Volume: 1, Page 5027 Paper number 9704
Abstract:
Semidefinite programs have received a great deal of attention because
of the variety of problems that they can model and the rich theory
that leads to polynomial-time algorithms to solve them. However, large
practical problems are still hard to solve because most algorithms
ignore the structure of the problem. In this paper we present an algorithm
for solving semidefinite programs that exploits structure yet is not
tailored a priori to any particular structure. It adapts a bundle
method designed to solve structured LMI feasibility problems. Duality
provides a tight lower bound for the optimal cost for use in a termination
criterion. A numerical experiment demonstrates that the complexity
is comparable to that of structured interior-point methods, and unlike
those methods it applies to a general class of structures.
Authors:
Anders Hansson,
Lieven Vandenberghe,
Volume: 1, Page 5033 Paper number 9042
Abstract:
In this article is discussed how to implement an efficient interior-point
algorithm for the semi-definite programs that result from integral
quadratic constraints. The algorithm is a primal-dual potential reduction
method, and the computational effort is dominated by a least-squares
system that has to be solved in each iteration. The key to an efficient
implementation is to utilize iterative methods and the specific structure
of integral quadratic constraints. The algorithm has been implemented
in Matlab. To give a rough idea of the efficiencies obtained, it is
possible to solve problems resulting in a linear matrix inequality
of dimension 130x130 with approximately 5000 variables in about 10
minutes on a lap-top. Problems with approximately 20000 variable and
a linear matrix inequality of dimension 230x230 are solved in a few
hours. It is not assumed that the system matrix has no eigenvalues
on the imaginary axis, nor is it assumed that it is Hurwitz.
Authors:
Giuseppe Calafiore,
Boris T. Polyak,
Volume: 1, Page 5035 Paper number 1415
Abstract:
In this paper, we discuss fast randomized algorithms for determining
an admissible solution for robust linear matrix inequalities (LMIs)
of the form F(x,(Delta)) (preceq) 0, where x is the optimization variable
and (Delta) is the uncertainty, which belongs to a given set (Delta).
The proposed algorithm is based on uncertainty randomization: it finds
a solution in a finite number of iterations with probability one, if
a strong feasibility condition holds. Otherwise, it computes a candidate
solution which minimizes the expected value of a suitably selected
feasibility indicator function. The theory is illustrated by examples
of application to uncertain linear inequalities and quadratic stability
of interval matrices.
Authors:
Jean B. Lasserre,
Volume: 1, Page 5041 Paper number 1111
Abstract:
We consider the general nonconvex quadratic programming problem and
provide a series of convex positive semidefinite programs (or LMI relaxations)
whose sequence of optimal values is monotone and converges to the optimal
value of the original problem. It improves and includes as a special
case the well-known Shor's relaxation. Often the optimal value is obtained
at some particular early relaxation as shown on some nontrivial test
problems.
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