A note on sufficient conditions forQ 0 andQ 0 ⋂P 0 matrices

In this note we settle an open problem posed by Al-Khayyal on a condition being sufficient for a matrix to belong to the class ofQ ₀-matrices. The answer is in the affirmative and we further relax the condition and obtain a sufficient condition forQ ₀-matrices. The results yield a class of matrices for which the linear complementarity problems can be solved as simple linear programs.     

On co-positive,semi-monotoneQ-matrices

In this paper we consider not necessarily symmetric co-positive as well as semi-monotoneQ-matrices and give a set of sufficient conditions for such matrices to beR ₀-matrices. We give several examples to show the sharpness of our results. Construction of these examples is based on the following elementary proposition: IfA is a square matrix of ordern whose first two rows are identical and bothA ₁₁ andA ₂₂ areQ-matrices whereA _ii stands for the principal submatrix ofA obtained by deleting rowi and columni fromA, thenA is aQ-matrix.Dedicated to our colleague and friend B. Ramachandran on his sixtieth birthday.Corresponding author.     

A note onQ-matrices

This paper concerns three classes of matrices that are relevant to the linear complementarity problem. We prove that within the class ofP ₀-matrices, theQ-matrices are precisely the regular matrices.Research supported by Department of Energy, Contract EY-76-S-03-0326 PA # 18.     

OnQ-matrices

In a recent paper [1], Aganagic and Cottle have established a constructive characterization for aP ₀-matrix to be aQ-matrix. Among the principal results in this paper, we show that the same characterization holds for anL-matrix as well, and that the symmetric copositive-plusQ-matrices are precisely those which are strictly copositive.     

Integral modular data and congruences

We compute all fusion algebras with symmetric rational S-matrix up to dimension 12. Only two of them may be used as S-matrices in a modular datum: the S-matrices of the quantum doubles of ℤ/2ℤ and S ₃. Almost all of them satisfy a certain congruence which has some interesting implications, for example for their degrees. We also give explicitly an infinite sequence of modular data with rational S- and T-matrices which are neither tensor products of smaller modular data nor S-matrices of quantum doubles of finite groups. For some sequences of finite groups (certain subdirect products of S ₃,D ₄,Q ₈,S ₄), we prove the rationality of the S-matrices of their quantum doubles.     

Fully copositive matrices

The class of fully copositive (C ₀ ^f ) matrices introduced in [G.S.R. Murthy, T. Parthasarathy, SIAM Journal on Matrix Analysis and Applications 16 (4) (1995) 1268–1286] is a subclass of fully semimonotone matrices and contains the class of positive semidefinite matrices. It is shown that fully copositive matrices within the class ofQ ₀-matrices areP ₀-matrices. As a corollary of this main result, we establish that a bisymmetricQ ₀-matrix is positive semidefinite if, and only if, it is fully copositive. Another important result of the paper is a constructive characterization ofQ ₀-matrices within the class ofC ₀ ^f . While establishing this characterization, it will be shown that Graves's principal pivoting method of solving Linear Complementarity Problems (LCPs) with positive semidefinite matrices is also applicable toC ₀ ^f Q ₀ class. As a byproduct of this characterization, we observe that aC ₀ ^f -matrix is inQ ₀ if, and only if, it is completelyQ ₀. Also, from Aganagic and Cottle's [M. Aganagic, R.W. Cottle, Mathematical Programming 37 (1987) 223–231] result, it is observed that LCPs arising fromC ₀ ^f Q ₀ class can be processed by Lemke's algorithm. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.Corresponding author.     

A unification of two classes ofQ-matrices

This note presents a class ofQ-matrices which includes Saigal's classN ofQ-matrices with negative principal minors and the classE of strictly semi-monotoneQ-matrices.Research supported by the Office of Naval Research under Contract N00014-75-C-0621 NR 047-048.     

Contraction Integrated Semigroups and Their Application to Continuous-time Markov Chains

We introduce the notion of the contraction integrated semigroups and give the Lumer-Phillips characterization of the generator, and also the charaterazied generators of isometric integrated semigroups. For their application, a necessary and sufficient condition for q-matrices Q generating a contraction integrated semigroup is given, and a necessary and sufficient condition for a transition function to be a Feller-Reuter-Riley transition function is also given in terms of its q-matrix.     

Signsolvability revisited

For a real matrix A, Q(A) denotes the set of all matrices with the same sign pattern as A. A linear system Ax=b is signsolvable if solvability and Q(x) depend only on Q(A) and Q(b). The study of signsolvability can be decomposed into the study of L-matrices and of S-matrices, where A is an L-matrix [S-matrix] if the nullspace of each member of Q(A) is {0} [is a line intersecting the open positive orthant]. The problem of recognizing L-matrices is shown to be NP-complete, even in the [almost square] case. Recognition of square L-matrices was transformed into a graph-theoretic problem by Bassett, Maybee, and Quirk in 1968. The complexity of this problem remains open, but that of some related graph-theoretic problems is determined. The relation between S-matrices and L-matrices is studied, and it is shown that a certain recursive construction yields all S-matrices, thus proving a 1964 conjecture of Gorman.     

<Emphasis FontCategory="NonProportional">L</Emphasis>-Matrices and solvability of linear complementarity problems by a linear program-Matrices and solvability of linear complementarity problems by a linear program

The classes ofL ₁-matrices,L ₂-matrices,L ₃-matrices andW-matrices are introduced to study solvability of a linear complementarity problem via solving a linear program. Three sufficient conditions are presented to guarantee that a linear complementarity problem is solvable via a linear program. The new sufficient conditions are weaker than the ones introduced by Mangasarian. This fact is also illustrated by an example. Partially supported by NSFC. This author is also with College of Business Administration of Human University as a Lotus chair professor.     

Quasi-compactness and absolutely continuous kernels

We show how the essential spectral radius r _e (Q) of a bounded positive kernel Q, acting on bounded functions, is linked to the lower approximation of Q by certain absolutely continuous kernels. The standart Doeblin’s condition can be interpreted in this context, and, when suitably reformulated, it leads to a formula for r _e (Q). This results may be used to characterize the Markov kernels having a quasi-compact action on a space of measurable functions bounded with respect to some test function, when no irreducibilty and aperiodicity are assumed.      

Q-matrices and spherical geometry

A real n × n matrix M is a Q-matrix if the linear complementarity problem w ? Mz=q, w ? 0, z ? 0, w^tz=0 has a solution for all real n-vectors q. M is nondegenerate if all its principal minors are nonzero. Spherical geometry is applied to the problem of characterizing nondegenerate Q-matrices. The stability of 3 × 3 nondegenerate Q-matrices and a generalization of the partitioning property of P-matrices are rather easily proved using spherical geometry. It is also proved that the set of 4 × 4 nondegenerate Q-matrices is not open.     

Necessary and sufficient conditions for the existence of complementary solutions and characterizations of the matrix classesQ andQ 0

We simplify a result by Mangasarian on the existence of solutions to the linear complementarity problem. The simplified condition gives a new geometric interpretation of the result. When used to characterize the matrix classesQ andQ ₀, our condition suggests a finitely checkable sufficient condition forP andP ₀.This work was supported in part by the Office of Naval Research under Contract No. N00014-86-K-0173, and by general research development funds provided by the Georgia Institute of Technology.     

Generalized composition and Volterra type operators between QK spaces

Abstract

In this paper, the boundedness and compactness of the generalized composition operators and the products of Volterra type operators a nd composition operators between Q_K spaces are investigated. We also give a necessary condition for multiplication operators between Q_K spaces to be bounded or compact.     

Q-functions of Hermitian Contractions of Krein-Ovcharenko Type

In this paper operator-valued Q-functions of Krein-Ovcharenko type are introduced. Such functions arise from the extension theory of Hermitian contractive operators A in a Hilbert space ℌ. The definition is related to the investigations of M.G. Krein and I.E. Ovcharenko of the so-called Q_μ- and Q_M-functions. It turns out that their characterizations of such functions hold true only in the matrix valued case. The present paper extends the corresponding properties for wider classes of selfadjoint contractive extensions of A. For this purpose some peculiar but fundamental properties on the behaviour of operator ranges of positive operators will be used. Also proper characterizations for Q_μ- and Q_M-functions in the general operator-valued case are given. Shorted operators and parallel sums of positive operators will be needed to give a geometric understanding of the function-theoretic properties of the corresponding Q-functions.     

A general RLC system with complex values

We study a semilinear second-order ordinary differential equation for a complex valued function Q which describes the evolution of a generalized RLC system over an interval [0,?T?]. We solve the Dirichlet and periodic problems under appropriate conditions. Moreover, we give conditions in order to ensure that any solution satisfying an initial condition Q(0)?=?Q ₀, Q′(0)=?I ₀ is defined over [0,?T?].     

On Generalized Friedrichs and Krein‐von Neumann Extensions and Canonical Systems

Let S be a densely defined and closed symmetric relation in a Hilbert space ℋ︁ with defect numbers (1,1), and let A be some of its canonical selfadjoint extensions. According to Krein's formula, to S and A corresponds a so‐called Q‐function from the Nevanlinna class N . In this note we show to which subclasses N _γ of N the Q‐functions corresponding to S and its canonical selfadjoint extensions belong and specify the Q‐functions of the generalized Friedrichs and Krein‐von Neumann extensions. A result of L. de Branges implies that to each function Q ∈ N there corresponds a unique Hamiltonian H such that Q is the Titchmarsh‐Weyl coefficient of the two‐dimensional canonical system J_y′ = —zHy on [0, ∞) where Weyl's limit point case prevails at ∞. Then the boundary condition y(0) = 0 corresponds to a symmetric relation T_min with defect numbers (1,1) in the Hilbert space L²_H, and Q is equal to the Q‐function with respect to the extension corresponding to the boundary condition y₁(0) = 0. If H satisfies some growth conditions at 0 or ∞, wepresent results on the corresponding Q‐functions and show under which conditions the generalized Friedrichs or Krein‐von Neumann extension exists.     

Q-matrices and boundedness of solutions to linear complementarity problems

This paper is concerned with the existence and boundedness of the solutions to the linear complementarity problemw=Mz+q,w0,z0,w ^T z=0, for eachq ⁿ . It has been previously established that, ifM is copositive plus, then the solution set is nonempty and bounded for eachq ⁿ iffM is aQ-matrix. This result is shown to be valid also forL ₂-matrices,P ₀-matrices, nonnegative matrices, andZ-matrices.     

Idempotent matrix lattices over distributive lattices

In this paper, the partially ordered set of idempotent matrices over distributive lattices with the partial order induced by a set of lattice matrices is studied. It is proved that this set is a lattice; the formulas for meet and join calculation are obtained. In the lattice of idempotent matrices over a finite distributive lattice, all atoms and coatoms are described. We prove that the lattice of quasi-orders over an n-element set Qord(n) is not graduated for n ≥ 3 and calculate the greatest and least lengths of maximal chains in this lattice. We also prove that the interval ([I, J]_≤, ≤) of idempotent (n × n)-matrices over {ie879-01}-lattices is isomorphic to the lattice of quasi-orders Qord(n). Using this isomorphism, we calculate the lattice height of idempotent {ie879-02}-matrices. We obtain a structural criterion of idempotent matrices over distributive lattices. __________ Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 13, No. 4, pp. 121–144, 2007.     

Dual and Feller-Reuter-Riley transition functions

In this paper, we investigate duality and Feller-Reuter-Riley (FRR) property of continuous-time Markov chains (CTMCs). A criterion of dual q-functions is given in terms of their q-matrices. For a dual q-matrix Q, a necessary and sufficient conditions for the minimal Q-function to be a FRR transition function are also given. Finally, by using dual technique, we give a criterion of FRR Q-functions when Q is monotone.