Intervals of P-matrices and related matrices

We consider intervals of matrices with respect to the usual entrywise partial ordering. Necessary and sufficient conditions are given for an interval of matrices to contain only P-matrices (i.e. matrices having only positive principal minors) or related matrices.     

On strong Z-matrices

A strong Z-matrix is a Z-matrix with negative off-diagonal entries and nonnegative diagonal entries. In this article, for a nonsingular strong Z-matrix, we indicate a way to ascertain whether such a matrix has the Lipschitzian property or not.     

On square roots of M-matrices

The question of the existence and uniqueness of an M-matrix which is a square root of an M-matrix is discussed. The results are then used to derive some new necessary and sufficient conditions for a real matrix with nonpositive off diagonal elements to be an M-matrix.     

On energy conservation and P-stability

When applied to the classical dynamical equations, generally, conventional time-stepping methods cannot conserve the total energy exactly, but up to their algebraic order. To obtain an energy-conserving method, we add an energy calibrated parameter to some conventional ones. The periodic stability and phase-lag property of this type of energy-conserving methods are investigated in this note. Some numerical results are reported to illustrate our conclusions.     

On the LU decomposition of V-matrices

We show that the class of V-matrices, introduced by Mehrmann [6], which contains the M-matrices and the Hermitian positive semidefinite matrices, is invariant under Gaussian elimination.     

On the angular derivative and univalence

f . , , — , A f f(). , , f() 0 . , , ,A , f . , f() - f() . , , . (1976) ( ¦f(z)¦<1) . . (1969) ( ).     

On algebraic Riccati equations associated with M-matrices

We consider the algebraic Riccati equation for which the four coefficient matrices form an M-matrix K. When K is a nonsingular M-matrix or an irreducible singular M-matrix, the Riccati equation is known to have a minimal nonnegative solution and several efficient methods are available to find this solution. In this paper we are mainly interested in the case where K is a reducible singular M-matrix. Under a regularity assumption on the M-matrix K, we show that the Riccati equation still has a minimal nonnegative solution. We also study the properties of this particular solution and explain how the solution can be found by existing methods.     

On the existence of super P-groups

A finite group (G, ·) is said to be sequenceable if its elements can be arranged in a sequence a₀ = e, a₁, a₂,…, a_n?1 in such a way that the partial products b₀ = a₀, b₁ = a₀a₁, b₂ = a₀a₁a₂,…, b_n?1 = a₀a₁a₂ ··· a_n?1 are all distinct (and consequently are the elements of G in a new order). It is said to be R-sequenceable if its elements can be ordered in such a way that the partial products b₀ = a₀, b₁ = a₀a₁, b₂ = a₀a₁a₂,…, b_n?2 = a₀a₁a₂ ··· a_n?2 are all different and so that b_n?1 = a₀a₁a₂ ··· a_n?1 = b₀ = e. (in the first case, the ordering a₀,a₁,…,a_n?1 of the elements is said to be a sequencing of G and, in the second case, an R-sequencing of G.) It is a super P-group if every element of one particular coset hG′ of the derived group can be expressed as the product of the n elements of G in such a way that the orderings of the elements in these products are sequencings of G with the exception that, in the case that h = e, the element e of G′ must be expressed as a product of the n elements of G which forms an R-sequencing of G. It is proved that every non-Abelian group of order pq such that p has 2 as a primitive root, where p and q are distinct odd primes with p < q, is a super P-group. Also provided is evidence for the conjectures that all Abelian groups and all dihedral groups of doubly even order (except those of orders 4 and 8) are super P-groups.     

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.     

On univalence of two integral operators

In this work we consider two integral operators. The integral operators were constructed on the basis of the fact that the number of functions from the composition of the operators is the entire part of a complex number modulus.     

On P-quasigroups and decompositions of complete undirected graphs

In [2], A. Kotzig has introduced the concepts of P-groupoid and P-quasigroup and has shown how these concepts are related to the decomposition of a complete undirected graph into disjoint closed paths. To each closed path of the graph associated with a given P-quasigroup Q there corresponds a cyclic partial transversal in the Latin square L which is defined by the multiplication table of Q. In this paper, it is shown that cyclic transversals are connected with Hamiltonian decompositions of complete undirected graphs having an even number of vertices and a connection between the order of a particular type of P-quasigroup and the length of its cyclic partial transversals is established. An indirect connection with the work of Yap [4] is established via the concept of isotopy.     

On the univalence of an integral operator

In this work the author introduces a general integral operator and determines conditions for the univalence of this integral operator.     

On the univalence of the log-biharmonic mappings

In this paper, we establish the univalence and starlikeness connection between log-biharmonic mappings and logharmonic mappings.     

Some properties of Q-matrices

This paper deals with the class of Q-matrices, that is, the real n × n matrices M such that for every q ∈ $\text{R}$^n×1, the linear complementarity problem

$\text{Iw ? Mz = q}$

,

$\text{w ? 0, z ? 0, and w}{}^{\mathrm{T}}\text{z = 0}$

, has a solution. In general, the results are of two types. First, sufficient conditions are given on a matrix M so that M ∈ Q. Second, conditions are given so that M ? Q.     

Inverse M-matrices, II

This is an update of the 1981 survey by the first author. In the meantime, a considerable amount has been learned about the very special structure of the important class of inverse M-matrices. Developments since the earlier survey are emphasized, but we have tried to be somewhat complete; and, some results have not previously been published. Some proofs are given where appropriate and references are given for others. After some elementary preliminaries, results are grouped by certain natural categories.     

On classes of matrices containing M-matrices and hermitian positive semidefinite matrices

Two new classes of matrices are introduced, containing hermitian positive semi-definite matrices and M-matrices. The relation to other well-known classes such as ω and τ-matrices and weakly sign symmetric matrices is examined, and invariance properties are shown.     

Completely mixed games and M-matrices

Any non-singular M-matrix is a completely mixed matrix game with positive value. We exploit this property to give game-theoretic proofs of several well-known characterizations of such matrices. The same methods yield also many theorems on S₀-irreducible matrices that are closely related to M-matrices.     

Singular M-matrices and inverse positivity

For a matrix decomposable as A=sI?B, where B?0, it is well known that A^?1?0 if and only if the spectral radius ρ(B)>s. An extension of this result to the singular case ρ(B)=s is made by replacing A^?1 by [A+t(I?AA^D)]^?1, where A^D is the Drazin generalized inverse.     

Two properties of M-matrices

If A is an M-matrix with the property that some power of A is lower triangular, then A is lower triangular. An analogue of the Minkowski determinant theorem is proved for a subclass of the M-matrices.