Title: Weak solutions for a class of nonlinear integrodifferential equations Author: Ivan Soukup Department: Department of mathematical analysis Supervisor: RNDr. Tomáš Bárta, Ph.D. Supervisor's e-mail address: tomas.barta@mff.cuni.cz Abstract: The work investigates a system of evolutionary nonlinear partial integrodifferential equations in three dimensional space. In particular it stud- ies an existence of a solution to the system introduced in [1] with Dirichlet boundary condition and initial condition u0. We adopt the scheme of the proof from [9] and try to avoid the complications rising from the integral term. The procedure consists of an approximation of the convective term and an ap- proximation of the potentials of both nonlinearities using a quadratic function, proving the existence of the approximative solution and then returning to the original problem via regularity of the approximative solution and properties of the nonlinearities. The aim is to improve the results of the paper [1]. 1

The thesis deals with qualitative properties of solutions of singular initial value problems for ordinary differential and integrodifferential equations which occur in the theory of linear and nonlinear electrical circuits and the theory of therminionic currents. The research is concentrated especially on questions of existence and uniqueness of solutions, asymptotic estimates of solutions and modications of Adomian decomposition method for singular initial problems. Solution algoritms are derived for scalar differential equations of Lane-Emden type using Taylor series and modication of the Adomian decomposition method. For certain classes of nonlinear of integrodifferential equations asymptotic expansions of solutions are constructed in a neighbourhood of a singular point. By means of the combination of Wazewski's topological method and Schauder xed-point theorem there are proved asymptotic estimates of solutions in a region which is homeomorphic to a cone having vertex coinciding with the initial point. Using Banach xed-point theorem the uniqueness of a solution of the singular initial value problem is proved for systems of integrodifferential equations of Volterra and Fredholm type including implicit systems. Moreover, conditions of continuous dependence of a solution on a parameter are determined. Obtained results are presented in illustrative examples.