Positive extension and completion problems for a class of structured matrices

A class of matrices, defined by a displacement rank property, is introduced. Completion and extension problems are studied for matrices in this class, under certain positivity constraints. The extension problem is reduced to a standard interpolation problem for Schur matrix valued functions.     

Positive extension and completion problems for a class of structured matrices

A class of matrices, defined by a displacement rank property, is introduced. Completion and extension problems are studied for matrices in this class, under certain positivity constraints. The extension problem is reduced to a standard interpolation problem for Schur matrix valued functions.     

Controllability completion problems of partial upper triangular matrices

The main result of this paper states sufficient conditions for the existence of a completion A_c of an n × n partial upper triangular matrix A, such that the pair (A_cB) has prescribed controllability indices, being B an n×m matrix. If A is a partial Hessenberg matrix some conditions may be dropped. An algorithm that obtains a completion A_c of A such that pair (A_ce_k) is completely controllable, where e_k is a unit vector, is used to proof the results.     

Simultaneous decomplexification of a pair of complex matrices by a similarity transformation

The following question is treated: Under what conditions can complex n-by-n matrices A and B be made real by the same similarity transformation? It is shown that if the algebra generated by A and B contains a matrix with a simple real spectrum, then the problem of the simultaneous decomplexification of a matrix pair can be reduced to the decomplexification of a single matrix by a diagonal similarity transformation. From this result, sufficient conditions are derived for the possibility of simultaneous decomplexification. An example illustrating these conditions is given.     

On fractional powers of a pair of matrices and a plate-beam problem

In this paper we consider the transversal deflections of a dynamically-coupled Von Kármán system consisting of a plate which has a beam attached to its one edge. The problem is considered in the form of a non-linear evolution problem in a product space. We show the existence of a unique local solution by following a fractional powers approach to first construct a “weak” solution in a larger space. Regularity properties for this solution yield a unique local strong solution for the original boundary-value problem. This approach entails the introduction of fractional powers of a pair of matrices.     

The unitary completion and QR iterations for a class of structured matrices

We consider the problem of completion of a matrix with a specified lower triangular part to a unitary matrix. In this paper we obtain the necessary and sufficient conditions of existence of a unitary completion without any additional constraints and give a general formula for this completion. The paper is mainly focused on matrices with the specified lower triangular part of a special form. For such a specified part the unitary completion is a structured matrix, and we derive in this paper the formulas for its structure. Next we apply the unitary completion method to the solution of the eigenvalue problem for a class of structured matrices via structured QR iterations.

     

Simultaneous triangularization of a pair of matrices whose commutator has rank two

Let A,B be n×n matrices with entries in an algebraically closed field F of characteristic zero, and let C=AB?BA. It is shown that if C has rank two and AⁱB^jC^k is nilpotent for 0?i, j?n?1, 1?k?2, then A, B are simultaneously triangularizable over F. An example is given to show that this result is in some sense best possible.     

Completely positive completion of partial matrices whose entries are completely bounded maps

We study completion problems of partial matrices associated with a graph where entries are completely bounded maps on aC ^*-algebra. We characterize a graph for which every -partial completely positive matrix has a completely positive completion. As a special case we study -partial functional matrices. We give a necessary and sufficient condition for a -partial functional matrix to have a positive completion and a representation for such matrices. These generalize some results on inflated Schur product maps due to Paulsen, Power and Smith. As an application, we study completely positive completions of partial matrices whose entries are completely bounded multipliers of the Fourier algebra of a locally compact group.     

A criterion of diagonalizability of a pair of matrices over the ring of principal ideals by common row and separate column transformations

We establish that a pair A, B, of nonsingular matrices over a commutative domain R of principal ideals can be reduced to their canonical diagonal forms D ^A and D ^B by the common transformation of rows and separate transformations of columns. This means that there exist invertible matrices U, V _A, and V _B over R such that UAV _a=D^A and UAV _B=D^B if and only if the matrices B _*A and D _* ^B D^A where B _* 0 is the matrix adjoint to B, are equivalent.     

Barrelled spaces with a B-complete completion

Let (E, ) be a barrelled locally convex space. The aim of this paper is to describe the barrelled topologies on E weaker than . When the completion Ê of (E, ) is B-complete, various properties of the barrelled topologies weaker than are proved. Some examples are given to illustrate the possible situations.