Abstract Differential Equations

This monograph deals with linear differential equations in Banach and Hilbert spaces whose coefficients are linear unbounded operators. Looking for examples or applications, the most natural ones are found in the theory of partial differential equations: if to one of the variables is given a privilegiate position and all the others are put together obtains 'at once' an ordinary 'differential' equation with respect to the variable. Adding boundary conditions in order to ensure definiteness of the solutions can often be translated in terms of considering solutions in some convenient linear--often normed--function spaces.

The present article is based on the Fermi Lectures I gave in May, 1985, at Scuola Normale Superiore, Pisa, in which I discussed various methods for solving the Cauchy problem for abstract nonlinear differential equations of evolution type. Here I present a detailed exposition of one of these methods, which deals with “elliptic-hyperbolic” equations in the abstract form and which has applications, among other things, to mixed initial-boundary value problems for certain nonlinear partial differential equations, such as elastodynamic and Schrödinger equations.

This book introduces the treatment of linear and nonlinear (quasi-linear) abstract evolution equations by methods from the theory of strongly continuous semigroups. The theoretical part is accessible to graduate students with basic knowledge in functional analysis, with only some examples requiring more specialized knowledge from the spectral theory of linear, self-adjoint operators in Hilbert spaces. Emphasis is placed on equations of the hyperbolic type which are less often treated in the literature.

This book presents new accurate and efficient exponentially convergent methods for abstract differential equations with unbounded operator coefficients in Banach space. These methods are highly relevant for practical scientific computing since the equations under consideration can be seen as the meta-models of systems of ordinary differential equations (ODE) as well as of partial differential equations (PDEs) describing various applied problems. The framework of functional analysis allows one to obtain very general but at the same time transparent algorithms and mathematical results which then can be applied to mathematical models of the real world. The problem class includes initial value problems (IVP) for first order differential equations with constant and variable unbounded operator coefficients in a Banach space (the heat equation is a simple example), boundary value problems for the second order elliptic differential equation with an operator coefficient (e.g. the Laplace equation), IVPs for the second order strongly damped differential equation as well as exponentially convergent methods to IVPs for the first order nonlinear differential equation with unbounded operator coefficients. For researchers and students of numerical functional analysis, engineering and other sciences this book provides highly efficient algorithms for the numerical solution of differential equations and applied problems.

Differential Equations in Abstract Spaces

The theory of linear Volterra Integro-differental equations has been developing rapidly in the last three decades. This book provides an easy-to-read, concise introduction to the theory of ill-posed abstract Volterra Integro-differential equations. It is accessible to readers whose backgrounds include functions of one complex variable, integration theory and the basic theory of locally convex spaces. Each chapter is further divided into sections and subsections, and contains plenty of examples and open problems.

The theory of abstract differential equations is a new branch of operator theory and of ordinary differential equations. It is a rapidly developing area of mathematics, and this book presents new results at the forefront of research in this field. Based on the author's own work, this volume covers differential equations in abstract spaces, presenting new and some of the lesser known facts and propositions of the theory. It will be invaluable reading for postgraduate students and research workers in ordinary and partial differential equations, almost-periodic solutions, theory of semigroups of operators and evolution equations.