On Some Properties of Convex Matrix Sets Characterized by P -Matrices and Block P -Matrices

In this paper, we consider convex sets of real matrices and establish criteria characterizing these sets with respect to certain matrix properties of their elements. In particular, we deal with convex sets of P-matrices, block P-matrices and M-matrices, nonsingular and full rank matrices, as well as stable and Schur stable matrices. Our results are essentially based on the notion of a block P-matrix and extend and generalize some recently published results on this topic.     

Convex sets of nonsingular and P:-Matrices

We show that the set r(A,B) (resp. c(A,B) of square matrices whose rows (resp. columns) are the independent convex combinations of the rows (resp.columns) of real matrices A and B consists entirely of nonsingular matrices if and only if BA^-1(resp. B^-1A) is a P-matrix. This imrpoves a theorem on P-Matrices proven in [2] and [3], in the context of interval nonsingularity. We also show that every real P-matrix admits a representation BA^-1 with the above property. These reseults are only partially true for complex P-matrices. Based on them we obtain a characterizaiton of complex P-matrices in terms of block partitions.     

Ratios of affine functions

Aratio of affine functions is a function which can be expressed as the ratio of a vector valued affine function and a scalar affine functional. The purpose of this note is to examine properties of sets which are preserved under images and inverse images of such functions. Specifically, we show that images and inverse images of convex sets under such functions are convex sets. Also, images of bounded, convex polytopes under such functions are bounded, convex polytopes. In addition, we provide sufficient conditions under which the extreme points of images of convex sets are images of extreme points of the underlying domains. Of course, this result is useful when one wishes to maximize a convex function over a corresponding set. The above assertions are well known for affine functions. Applications of the results include a problem that concerns the control of stochastic eigenvectors of stochastic matrices.     

On the Separation and Order Law of Cancellation for Bounded Sets

In this paper we introduce the separation law for convex sets. Moreover, we prove that for a locally convex topological vector space the order cancellation law and separation law are equivalent.     

几种凸模糊集间的转换关系

在引用扎德所定义的凸模糊集、强凸模糊集、严格凸模糊集等概念的基础上，探讨了这三种凸模糊集间的转换条件，得到凸模糊集与强凸模糊集、强凸模糊集与严格凸模糊集间的等价条件。     

(∈,∈∨q)-n维凸模糊集

利用n维模糊集截集理论和模糊点与n维模糊集的邻属关系,并利用n+1-值Lukasiewicz蕴涵,首先给出(α,β)-n维凸模糊集的定义,然后对(∈,∈)-n维凸模糊集和(∈,∈∨q)-n维凸模糊集这两种非常有意义的n维凸模糊集进行了讨论,最后得到了一些有意义的结果。这将为n维凸模糊分析理论研究打下基础。     

Characterizations of minimal semipositivity

A real m×n matrix A is said to be semipositive if there is a nonnegative vector λ such that Ax exists and is componentwise positive. A is said to be minimally semipositive if it is semipositive and no proper m×p submatrix of A is semipositive. Minimal semipositivity is characterized in this paper and is related to rectangular monotonicity and weak r-monotonicity. P-matrices and nonnegative matrices will also be considered.     

Convex spectral functions

In this paper we characterize all convex functionals defined on certain convex sets of hermitian matrices and which depend only on the eigenvalues of matrices. We extend these results to certain classes of non-negative matrices. This is done by formulating some new characterizations for the spectral radius of non-negative matrices, which are of independent interest.     

Siegmund Duality for Continuous Time Markov Chains on ℤ<Stack><Subscript>+</Subscript><Superscript>d</Superscript></Stack>

For the continuous time Markov chain with transition function P(t) on Z₊^d, we give the necessary and sufficient conditions for the existence of its Siegmund dual with transition function P(t). If Q, the q-matrix of P(t), is uniformly bounded, we show that the Siegmund dual relation can be expressed directly in terms of q-matrices, and a sufficient condition under which the Q-function is the Siegmund dual of some Q-function is also given.     

M-matrix products having positive principal minors

Sufficient conditions are given for powers and products of M-matrices to have all principal minors positive. Several of these conditions involve directed graphs of the matrices. In particular we show that if A and B are irreducible M-matrices which have longest simple circuit of length two with A+B having no simple circuit longer than three, then the product AB has all principal minors positive.     

On approximating the nearest Ω‐stable matrix

In this paper, we consider the problem of approximating a given matrix with a matrix whose eigenvalues lie in some specific region Ω of the complex plane. More precisely, we consider three types of regions and their intersections: conic sectors, vertical strips, and disks. We refer to this problem as the nearest Ω‐stable matrix problem. This includes as special cases the stable matrices for continuous and discrete time linear time‐invariant systems. In order to achieve this goal, we parameterize this problem using dissipative Hamiltonian matrices and linear matrix inequalities. This leads to a reformulation of the problem with a convex feasible set. By applying a block coordinate descent method on this reformulation, we are able to compute solutions to the approximation problem, which is illustrated on some examples.     

Stability of m-matrix products

We investigate various types of stability for powers and products of nonsingular M-matrices. Stability of the matrix powers is categorized according to the length of the longest simple circuit in the digraph of the matrix, while stability of the general products is categorized by the order of the matrices. Additional results are given regarding stability of the Hadamard product of M-matrices and for matrices whose digraph has a longest simple circuit of length two.     

几种新的截集及其应用

本文从“邻域”和“重域”的观点出发引入了三种新的截集：下截集，下重截集和上重截集。我们给出这些截集的性质及相应的分解定理，表现定理和扩展原理，作为应用，我们讨论了两方面的内容；一是利用落影表现理论，将一个模糊集看作“重云”的落影，然后用下生截集和落影表现理论来定义模糊集的运算，得到了与“２”一致的结果。     

Mixed dominating matrices

We characterize the class of matrices for which the set of supports of nonnegative vectors in the null space can be determined by the signs of the entries of the matrix. This characterization is in terms of mixed dominating matrices, which are defined by the nonexistence of square submatrices that have nonzeros of opposite sign in each row. The class of mixed dominating matrices is contained in the class of L-matrices from the theory of sign-solvability, and generalizes the class of S-matrices. We give a polynomial-time algorithm to decide if a matrix is mixed dominating. We derive combinatorial conditions on the face lattice of a Gale transform of a matrix in this class.     

On Graph-realizable Sets of Periods

We characterize sets of periods of cycles which arbitrary continuous graph maps may have. In this investigation, we need the spectral decomposition for graph maps [Blokh, A.M. "On dynamical systems on one-dimensional branched manifolds", Theory Funct. Funct. Anal. Appl. Kharkov 46 (1986) pp. 8-18 (Russian); 47 (1986) pp. 67-77; 48 (1987) pp. 32-46] briefly described in "The Spectral Decomposition" Section.     

The symmetric inverse M-matrix completion problem

Necessary and sufficient conditions are given on the data for completability of a partial symmetric inverse M-matrix, the graph of whose specified entries is a cycle, and these conditions coincide with those we identify to be necessary in the general (nonsymmetric) case. Graphs for which all partial symmetric inverse M-matrices have symmetric inverse M-matrix completions are identified and these include those that arise in the general (positionally symmetric) case. However, the identification of all such graphs is more subtle than the general case. Finally, we show that our new cycle conditions are sufficient for completability of all partial symmetric inverse M-matrices, the graph of whose specified entries is a block graph.     

Three notions of tropical rank for symmetric matrices

We introduce and study three different notions of tropical rank for symmetric and dissimilarity matrices in terms of minimal decompositions into rank 1 symmetric matrices, star tree matrices, and tree matrices. Our results provide a close study of the tropical secant sets of certain nice tropical varieties, including the tropical Grassmannian. In particular, we determine the dimension of each secant set, the convex hull of the variety, and in most cases, the smallest secant set which is equal to the convex hull.     

拟凸对策的解

本文先引入拟凸对策的概念作为凸对策的推广,然后研究这种对策的各种解的性质。我们主要证得,当局中人数小于6或者对策的复盖严格凸时,谈判集与核心重合,核是单点集。另外,存在一个6人拟凸对策,其谈判集与核心不同。     

On the number of disjoint convex quadrilaterals for a planar point set

For a given planar point set P, consider a partition of P into disjoint convex polygons. In this paper, we estimate the maximum number of convex quadrilaterals in all partitions.     

Dykstra's Algorithm for a Constrained Least-squares Matrix Problem

We apply Dykstra's alternating projection algorithm to the constrained least-squares matrix problem that arises naturally in statistics and mathematical economics. In particular, we are concerned with the problem of finding the closest symmetric positive definite bounded and patterned matrix, in the Frobenius norm, to a given matrix. In this work, we state the problem as the minimization of a convex function over the intersection of a finite collection of closed and convex sets in the vector space of square matrices. We present iterative schemes that exploit the geometry of the problem, and for which we establish convergence to the unique solution. Finally, we present preliminary numberical results to illustrate the performance of the proposed iterative methods.