Theory of Operator Matrices

Among all operators on a Hilbert space the class of normal operators are considered to be most well understood. The theory of normal operators is so successful that much of the theory of non-normal operators is modeled after it. A natural way to extend a successful theory is to weaken some of its hypothesis slightly and hope that the results are weakened only slightly. One weakening of normality is quasinormality. In this book we discuss such non-normal operators.