Finite Dimensional Algebras

The theory of finite-dimensional algebras is one of the most fundamental domains of modern algebra, applied in several other parts of mathematics andin theoretical physics. This book, written by two of the leading researchersin the field and revised and augmented for the English edition, was translated from the Russian by a third leading specialist, who has contributed to it an appendix. The book presents both the basic classical theory and more recent results closely related to current research (some category theory including Morita's theorem, schemes of quivers andtensor algebras, duality, quasi-Frobenius, hereditary, serial algebras). Theonly prior knowledge assumed of the reader is linear algebra and, in places,a little group theory. Each chapter includes a series of exercises, illustrating the content and introducing more refined results: for the more complicated ones, hints for the solution are given - thus the book can be used as a textbook in class or for self-study, and as an up-to-date reference to the field.

This English edition has an additional chapter "Elements of Homological Al gebra." Homological methods appear to be effective in many problems in the theory of algebras; we hope their inclusion makes this book more complete and self-contained as a textbook. We have also taken this occasion to correct several inaccuracies and errors in the original Russian edition. We should like to express our gratitude to V. Dlab who has not only metic ulously translated the text, but has also contributed by writing an Appendix devoted to a new important class of algebras, viz. quasi-hereditary algebras. Finally, we are indebted to the publishers, Springer-Verlag, for enabling this book to reach such a wide audience in the world of mathematical community. Kiev, February 1993 Yu.A. Drozd V.V. Kirichenko Preface The theory of finite dimensional algebras is one of the oldest branches of modern algebra. Its origin is linked to the work of Hamilton who discovered the famous algebra of quaternions, and Cayley who developed matrix theory. Later finite dimensional algebras were studied by a large number of mathematicians including B. Peirce, C.S. Peirce, Clifford, .Weierstrass, Dedekind, Jordan and Frobenius. At the end of the last century T. Molien and E. Cartan described the semisimple algebras over the complex and real fields and paved the first steps towards the study of non-semi simple algebras."

1. Introduction.- 1.1 Basic Concepts. Examples.- 1.2 Isomorphisms and Homomorphisms. Division Algebras.- 1.3 Representations and Modules.- 1.4 Submodules and Factor Modules. Ideals and Quotient Algebras.- 1.5 The Jordan-H lder Theorem.- 1.6 Direct Sums.- 1.7 Endomorphisms. The Peirce Decomposition.- Exerises to Chapter 1.- 2. Semisimple Algebras.- 2.1 Schur's Lemma.- 2.2 Semisimple Modules and Algebras.- 2.3 Vector Spaces and Matrices.- 2.4 The Wedderburn-Artin Theorem.- 2.5 Uniqueness of the Decomposition.- 2.6 Representations of Semisimple Algebras.- Exercises to Chapter 2.- 3. The Radical.- 3.1 The Radical of a Module and of an Algebra.- 3.2 Lifting of Idempotents. Principal Modules.- 3.3 Projective Modules and Projective Covers.- 3.4 The Krull-Schmidt Theorem.- 3.5 The Radical of an Endomorphism Algebra.- 3.6 Diagram of an Algebra.- 3.7 Hereditary Algebras.- Exercises to Chapter 3.- 4. Central Simple Algebras.- 4.1 Bimodules.- 4.2 Tensor Products.- 4.3 Central Simple Algebras.- 4.4 Fundamental Theorems of the Theory of Division Algebras.- 4.5 Subfields of Division Algebras. Splitting Fields.- 4.6 Brauer Group. The Frobenius Theorem.- Exercises to Chapter 4.- 5. Galois Theory.- 5.1 Elements of Field Theory.- 5.2 Finite Fields. The Wedderburn Theorem.- 5.3 Separable Extensions.- 5.4 Normal Extensions. The Galois Group.- 5.5 The Fundamental Theorem of Galois Theory.- 5.6 Crossed Products.- Exercises to Chapter 5.- 6. Separable Algebras.- 6.1 Bimodules over Separable Algebras.- 6.2 The Wedderburn-Malcev Theorem.- 6.3 Trace, Norm, Discriminant.- Exercises to Chapter 6.- 7. Representations of Finite Groups.- 7.1 Maschke's Theorem.- 7.2 Number and Dimensions of Irreducible Representations.- 7.3 Characters.- 7.4 Algebraic Integers.- 7.5 Tensor Products of Representations.- 7.6 Burnside's Theorem.- Exercises to Chapter 7.- 8. The Morita Theorem.- 8.1 Categories and Functors.- 8.2 Exact Sequences.- 8.3 Tensor Products.- 8.4 The Morita Theorem.- 8.5 Tensor Algebras and Hereditary Algebras.- Exercises to Chapter 8.- 9. Quasi-Frobenius Algebras.- 9.1 Duality. Injective Modules.- 9.2 Lemma on Separation.- 9.3 Quasi-Frobenius Algebras.- 9.4 Uniserial Algebras.- Exercises to Chapter 9.- 10. Serial Algebras.- 10.1 The Nakayama-Skornjakov Theorem.- 10.2 Right Serial Algebras.- 10.3 The Structure of Serial Algebras.- 10.4 Quasi-Frobenius and Hereditary Serial Algebras.- Exercises to Chapter 10.- 11. Elements of Homological Algebra.- 11.1 Complexes and Homology.- 11.2 Resolutions and Derived Functors.- 11.3 Ext and Tor. Extensions.- 11.4 Homological Dimensions.- 11.5 Duality.- 11.6 Almost Split Sequences.- 11.7 Auslander Algebras.- Exercises to Chapter 11.- References.- A.1 Preliminaries. Standard and Costandard Modules.- A.3 Basic Properties.- A.4 Canonical Constructions.- A.6 Final Remarks.- References to the Appendix.