Almost periodic solutions of differential equations in by Yoshiyuki Hino, Toshiki Naito, Nguyen VanMinh, Jong Son Shin

By Yoshiyuki Hino, Toshiki Naito, Nguyen VanMinh, Jong Son Shin

This monograph provides fresh advancements in spectral stipulations for the lifestyles of periodic and virtually periodic options of inhomogenous equations in Banach areas. a few of the effects symbolize major advances during this quarter. particularly, the authors systematically current a brand new method in response to the so-called evolution semigroups with an unique decomposition process. The booklet additionally extends classical innovations, comparable to mounted issues and balance equipment, to summary sensible differential equations with purposes to partial practical differential equations. nearly Periodic strategies of Differential Equations in Banach areas will entice somebody operating in mathematical research.

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371] . 3 In the case where 9 = AP(X ) the condition iv) in Theorem 1 . 20 can be replaced by the condition that X does not contain Co (see [8, Proposition 3 . 1 , p . 369]) . Another alternative o f the condition iv) i s the total ergodicity of u which i s defined as follows: u E BUC(R, X ) i s called totally ergodic if M1Ju := lim T -+ OO 1 27 - j T -T . 6] , [192] ) . Another case i n which the condition iv) can b e dropped is that sp(u) is discrete (see [12] ) . From this remark the following example is obvious: Example 1 .

We consider the equation ( 2 . 10 ) AX - P(t)x = y , where y E X is given. If X is a solution to Eq. 1O ) , then AX y + w , where U(t, O) (A - P) � l U ( I , t)y. Conversely, defining X by this equation, it follows that (A - P(t))x = y so p(P(t) ) :::> p(P) \ {O} . The second assertion follows by the periodicity. Finally, the above formula involving x proves the third assertion. 2 In view of the above lemma, below, in connection with spectral prop­ erties of the monodromy operators, the terminology " monodromy operators" may be referred to as the operator P if this does not cause any danger of confusion.

15 sp(f) C I1b (f) . 4. A Spectral Criterion for Almost Periodicity of a Function Suppose that we know beforehand that f E BUC ( R, X). It is often possible to establish the almost periodicity of this function starting from certain a priori infor­ mation about its spectrum. CHAPTER 1 . PRELIMINARIES 29 Theorem 1 . 2 0 Let £ and 9 be closed, translation invariant subspaces of the space BUC(R, X ) and suppose that i) 9 c £ ,- ii) 9 contains all constant functions which belong to £ ,iii) £ and 9 are invariant under multiplications by e i e · for all � E R,­ iv) whenever f E 9 and F E £, where F(t) = J� f (s)ds, then F E g .

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