Wellposedness of the Cauchy problems for hyperbolic systems with large data

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1. Semigroups of locally Lipschitz operators are characterized by subtangential conditions and semilinear stability conditions in terms of a family of metric-like functionals. The result is applied to the mixed problem for the complex Ginzburg-Landau equation.2. It is interesting to compute solutions of Cauchy problems for partial differential equations numerically and to discuss the question of convergence which arises in that case. Such problems are treated by the theory of semigroups of operators. A convergence theorem and an approximation theorem for semigroups of Lipschitz operators are given. These theorems are applied to a semi-discrete approximation problem for a quasi-linear wave equation with damping and a finite difference method for a quasi-linear equation of Kirchhoff type.3. An approximation theorem is given for abstract quasi-linear evolution equations in the sense of Hadamard. The result is applied to an approximation problem for a degenerate Kirchhoff equation.4. The situation that the domains of differential operators are not dense in the underlying space arises when the mixed problems for certain partial differential equations in the space of continuous functions are studied. This leads to the study of the abstract Cauchy problems for quasi-linear evolution equations with non-densely defined operators. The result is applied to obtain the global wellposedness for quasi-linear wave equations of Kirchhoff type with acoustic boundary conditions and the local solvability of quasi-linear wave equations with Wentzell boundary conditions in the space of continuous functions.