A collection of matrices is said to be triangularizable if there is an invertible matrix S such that S1 AS is upper triangular for every A in the collection. This generalization of commutativity is the subject of many classical theorems due to Engel, Kolchin, Kaplansky, McCoy and others. The concept has been extended to collections of bounded linear operators on Banach spaces: such a collection is defined to be triangularizable if there is a maximal chain of subspaces of the Banach space, each of which is invariant under every member of the collection. Most of the classical results have been generalized to compact operators, and there are also recent theorems in the finite-dimensional case. This book is the first comprehensive treatment of triangularizability in both the finite and infinite-dimensional cases. It contains numerous very recent results and new proofs of many of the classical theorems. It provides a thorough background for research in both the linear-algebraic and operator-theoretic aspects of triangularizability and related areas. More generally, the book will be useful to anyone interested in matrices or operators, as many of the results are linked to other topics such as spectral mapping theorems, properties of spectral radii and traces, and the structure of semigroups and algebras of operators. It is essentially self-contained modulo solid courses in linear algebra (for the first half) and functional analysis (for the second half), and is therefore suitable as a text or reference for a graduate course.

In recent years there has been a large amount of work on invariant subspaces, motivated by interest in the structure of non-self-adjoint of the results have been obtained in operators on Hilbert space. Some the context of certain general studies: the theory of the characteristic operator function, initiated by Livsic; the study of triangular models by Brodskii and co-workers; and the unitary dilation theory of Sz. Nagy and Foia!? Other theorems have proofs and interest independent of any particular structure theory. Since the leading workers in each of the structure theories have written excellent expositions of their work, (cf. Sz.-Nagy-Foia!? [1], Brodskii [1], and Gohberg-Krein [1], [2]), in this book we have concentrated on results independent of these theories. We hope that we have given a reasonably complete survey of such results and suggest that readers consult the above references for additional information. The table of contents indicates the material covered. We have restricted ourselves to operators on separable Hilbert space, in spite of the fact that most of the theorems are valid in all Hilbert spaces and many hold in Banach spaces as well. We felt that this restriction was sensible since it eases the exposition and since the separable-Hilbert space case of each of the theorems is generally the most interesting and potentially the most useful case.

This volume is designed to appeal to two different, yet intersecting audiences: linear algebraists and operator theorists. The first half contains a thorough treatment of classical and recent results on triangularization of collections of matrices, while the remainder describes what is known about extensions to linear operators on Banach spaces. It will thus be useful to everyone interested in matrices or operators since the results involve many other topics.

All memoirs bring the past into the present, but only a few manage to illuminate both simultaneously. This quietly insightful masterpiece of remembrance belongs in that select group. Heydar Radjavi's evocations of growing up in Tabriz in the 1930s and 1940s describe a traditionalist Iran grappling with modernity, a process as fraught with contradictions and stresses then as it is in Iran today. In a series of mini-tales, we meet a rich cast of characters: the elderly father who works in the Tabriz bazaar and runs his household according to unbending religious precepts; the resourceful mother who finds ways to enjoy such forbidden frivolities as music; the female playmate who marries at the age of nine; the teacher whose personal journey takes him from strictest piety to political radicalism; and, many more. Finding a path through all the complexities is Radjavi himself - a wide-eyed little boy in some episodes, an adventurous teenager in others, and finally a young man preparing to enter a fast-changing world. The tone is always light, the memories wonderfully vivid, and the underlying theme of tension between old and new truly timeless.