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Convergence theorems for integrated semigroups. (English) Zbl 0786.47036

The paper provides approximation results for the abstract homogeneous \[ {du\over dt}=Au,\quad u(0)= u_ 0,\tag{1} \] and nonhomogeneous \[ {du\over dt}= Au(t)+ f(t),\quad u(0)=x\tag{2} \] Cauchy problems. The novelty consists in the search for integral solutions to (1) and (2). Then \(u(t)\) satisfies the integrated equation \[ u(t)= u_ 0+ A \int^ t_ 0 u(s)ds,\tag{3} \] in the case (1), and \[ u(t)= x+ A\int^ t_ 0 u(s)ds+ \int^ t_ 0 f(s)ds,\tag{4} \] in the second case. This idea was introduced by G. Da Prato and E. Sinestrari [Ann. Sc. Norm. Sup. Pisa, Cl. Sci., IV. Ser. 14, No. 2, 285-344 (1987; Zbl 0652.34069)]. It is useful when \(u_ 0\) and \(x\) are not sufficiently regular. The main theorem formulated and proved in the present paper concerns the generalization of the famous Trotter-Kato theorem of semigroup theory. In the case under study it states that resolvent consistency, under appropriate conditions, implies convergence of integral solutions. One simple example illustrates the possibility of application to the population model.
The paper is clearly written and of interest to specialists in differential equations in Banach spaces.

MSC:

47D06 One-parameter semigroups and linear evolution equations
35A35 Theoretical approximation in context of PDEs
35C15 Integral representations of solutions to PDEs
35G10 Initial value problems for linear higher-order PDEs
35K25 Higher-order parabolic equations

Citations:

Zbl 0652.34069
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