121609264
A combined direct-iterative approach for solving large scale singular and rectangular consistent systems of linear equations
Abstract We construct a certain iterative scheme for solving large scale consistent systems of linear equations Ax = b , (*) where A is a complex m X n matrix of rank r , m ⩾ n , and where A is assumed reasonably well conditioned. The iterative method is obtained through a careful exploitation of an LU -decomposition of A , and, disregarding roundoff errors, it converges to a solution to ( * ), though not necessarily the minimal l 2 -norm one, from any starting vector in r iterations. Moreover, once the LU -decomposition of A is complete, only about r 3 /2 arithmetic operations (multiplications and divisions) are needed to execute the r iterations.
120219316
On bounds for the convergence of the SSOR method for H-matrices
In [1] G. Alefeld and R S. Varga show that if A is an H-matrix, then where and JA are, respectively, the SSOR and the Jacobi iteration matrices associated with A. We investigate the possibility for[M0001] when Ais an H-matrix and show that unless does not hold. Comparison is made with the sharpness of a similar bound on the ω's for which the SOR iteration matrix associated with A converges.
2662369
CONVERGENCE OF INFINITE PRODUCTS OF MATRICES AND INNER{OUTER ITERATION SCHEMES
We develop conditions under which a product Q1=0 Ti of matrices chosen from a possibly innite set of matricesS =fTjjj2 Jg converges. We obtain the following conditions which are sucient for the convergence of the product: There exists a vector norm such that all matrices in S are nonexpansive with respect to this norm and there exists a subsequencefikg 1=0 of the sequence of the nonnegative integers such that the corresponding sequence of operators Tik 1=0 converges to an operator which is paracontracting with respect to this norm. We deduce the continuity of the limit of the product of matrices as a function of the sequencesfikg1=0 . But more importantly, we apply our results to the question of the convergence of inner{outer iteration schemes for solving singular consistent linear systems of equations, where the outer splitting is regular and the inner splitting is weak regular.
120901930
Nonnegative jordan bases
In this paper we are concerned with the problem of when the generalized eigenspace of an n × n nonegative matrix A corresponding to its spectrai radius ρ has a nonnegative Jordan basis. Richman and Schneider have shown this to hold when, and only when, the Weyr characteristics of A corresponding to ρ is equal to the vector of levels in the singular graph of A Here we develop sufficient conditions for this equality to hold based upon the linear independence of a certain set of vectors which are generated according to a process of elimination of totally independent chains from the singular graph. We show that this condition comes close to being a further characterization for the existence of a nonnegative Jordan basis for this eigenspace and actually conjecture that this is the case. Finally, we show that this eigenspace has a Rothblum basis which is a Jordan basis if and only if the singular graph is a disjoint union of chains.
121748192
A note on generalizations of strict diagonal dominance for real matrices
Abstract We investigate classes of real square matrices possessing some weakened from of strict diagonal dominance of a real matrix whose diagonal entries are all positive. The intersection of each one of these classes with the set of all real matrices, with nonpositive off-diagonal elements, coincides with the set of all nonsingular M - matrices.
120746270
On the square roots of strictly quasiaccretive complex matrices
Abstract The square roots of a complex n × n matrix A for which the real part of e ix A , where χϵ[ −π 2 , π 2 ] , is positive definite are investigated. It is shown, for example, that when χ= −π 2 (i.e., A is strictly dissipative), A has a unique square root whose real and imaginary parts are both positive definite.
120497198
A maximality theorem concerning extreme points
118524160
Automatic Continuity of Linear Operators
The present survey is essentially based on some recent automatic continuity results which have been obtained by Ernst Albrecht and the author in the joint papers [1;2;3]. In contrast to the excellent account of automatic continuity theory in Sinclair's lecture notes [29] and in Dales' recent survey article [9], the emphasis of the present exposition lies on the automatic continuity problem for linear operators acting between spaces of functions and distributions. The continuity of such operators will be derived from certain conditions which naturally arise in the theory of linear systems, namely from time-invariance and causality on the one side and from dissipativity on the other. The automatic continuity of all time-invariant and causal linear operators turns out to be just one achievement of a far-reaching new theory on automatic continuity which also applies to the problem of continuity for algebrahomomorphisms, derivations, intertwining operators, and local operators. Some central features of this theory will be sketched; in particular, some extensions and variants of the classical principle of uniform boundedness will be discussed.
122589104
Bemerkungen zum von Neumannschen Minimaxtheorem
123207765
On the Strassen disintegration theorem
120206552
Beschränktheitsaussagen für sublineare und bisublineare Funktionale