- About this Journal ·
- Abstracting and Indexing ·
- Aims and Scope ·
- Annual Issues ·
- Article Processing Charges ·
- Author Guidelines ·
- Bibliographic Information ·
- Citations to this Journal ·
- Contact Information ·
- Editorial Board ·
- Editorial Workflow ·
- Free eTOC Alerts ·
- Publication Ethics ·
- Recently Accepted Articles ·
- Reviewers Acknowledgment ·
- Submit a Manuscript ·
- Subscription Information ·
- Table of Contents
Abstract and Applied Analysis
Volume 2012 (2012), Article ID 180894, 17 pages
Almost Periodic (Type) Solutions to Parabolic Cauchy Inverse Problems
Department of Mathematics, Harbin Institute of Technology, Harbin 150001, China
Received 23 December 2011; Revised 1 March 2012; Accepted 12 March 2012
Academic Editor: István Györi
Copyright © 2012 Fenglin Yang and Chuanyi Zhang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
We first show the existence and uniqueness of (pseudo) almost periodic solutions of some types of parabolic equations. Then, we apply the results to a type of Cauchy parabolic inverse problems and show the existence, uniqueness, and stability.
Zhang in [1, 2] defined pseudo almost periodic functions. As almost periodic functions, pseudo almost periodic functions are applied to many mathematical areas, particular to the theory of ordinary differential equations. (e.g., see [3–26] and references therein). However, the study of the related topic on partial differential equations has only a few important developments. On the other hand, almost periodic functions to various problems have been investigated (e.g., see [27–32] and references therein), but little has been done about the inverse problems except for our work in [33–36]. In , we study pseudo almost periodic solutions to parabolic boundary value inverse problems. In this paper, we devote such solutions to cauchy problems.
To this end, we need first to define the spaces in a more general setting. Let . Let (resp., , where ) denote the algebra of bounded continuous complex-valued functions on (resp. with the supremum norm. For (resp., ) and , the translation of by is the function (resp., .
Definition 1.1. (1) A function is called almost periodic if for every the set
is relatively dense in . Denote by the set of all such functions. The number (vector) is called translation number (vector) of .
(2) A function is said to be almost periodic in and uniform on compact subsets of if for each and is uniformly continuous on for any compact subset . Denote by the set of all such functions. For convenience, such functions are also called uniformly almost periodic.
(3) A function is called pseudo almost periodic if where and , uniformly with respect to , where is any compact subset of . Denote by the set of all such functions.
Members of are called almost periodic type.
We will use the notations throughout the paper: . means that is almost periodic type in and uniformly for means that is almost periodic type in and uniformly for .
Let be the fundamental solution of the heat equation .
In the next section, we will show the existence and uniqueness of some type of parabolic equations. Sections 3 is devoted to a type of Cauchy Problem respectively.
2. Solutions of Parabolic Equations
Lemma 2.1. Let . If and then for each fixed .
Proof. First consider the case that . Let be an translation vector of :
where is the zero vector. Note that, we get
where and with a bounded subset of . This shows that .
To show that if , we only need to show that if . That is, uniformly with respect to , here is any compact subset of .
Since , for there exist positive numbers and such that, when for all and , one has Therefore, uniformly with respect to , where by we mean that This shows that . The proof is complete.
Corollary 2.2. Let , and let be as in Lemma 2.1. Then, .
Proof. Note that
By Lemma 2.1 we get the conclusion.
Lemma 2.3. If and then and are all in .
The proof is similar to that of Lemma 2.1, so we omit it.
Theorem 2.4. Consider the heat problem If are in and are in , then (2.10) has a unique solution .
Proof. Problem (2.10) has the standard solution (see ):
and is the parabolic operator
Now, we show that
By Lemmas 2.1 and 2.3, .
Obviously, By Lemmas 2.1 and 2.3 we only need to show that the functions are in . We do this by induction. By Lemmas 2.1 and 2.3 and Corollary 2.2, it is true for the case . Suppose that . Then, By the induction assumption and Lemma 2.3, we have . Similarly one shows that . The proof is complete.
3. Cauchy Problem
Starting this section we will apply the results of the last section to inverse problems of partial differential equations. We will investigate two types of initial value problems in this and the next sections, respectively. We will keep the notation in Section 2 and, at the same time, introduce the following new notation:
The following estimates are easily obtained: where are positive and increasing for and as .
To show the main results of this and the next sections, the following lemmas are needed. The first lemma is the Gronwall-Bellman lemma; the convenient reference should be an ODE text, for instance, it is proved on page 15 of .
Lemma 3.1. Let , , and be real, continuous functions on with . If then
Lemma 3.2. Let be a continuous function on . If , , and are nondecreasing and nonnegative on and then where
Proof. Replacing in the two integrals of (*) by the expression on the right-hand side in (26), changing the integral order of the resulting inequality, and making use of the monotonicity of , , and , one gets Using Lemma 3.1 leads to the conclusion.
Lemma 3.3. Let and . If is a solution of the problem then where .
One sees that depends on only and is bounded near zero.
Proof. The solution can been written as so, By Lemma 3.1 one gets the desired result. The proof is complete.
Problem 1. Find functions and such that where , and . are constants.
We have the following additional problem.
Problem 2. Find functions and such that
The Cauchy problems with unknown coefficient belong to inverse problems . “In the last two decades, the field of inverse problems has certainly been one of the fastest growing areas in applied mathematics. This growth has largely been driven by the needs of applications both in other sciences and in industry.” . For the two problems above, we have the following.
Proof. Let . Then, satisfies
So, if Problem 1 has a solution , then Problems (3.18)–(3.20) have the solution with . Obviously if .
On the other hand, if and satisfy (3.18)–(3.20), then we will show that Problem 1 has a unique solution and .
The uniqueness comes from the uniqueness of Cauchy Problem (1)-(2). For the existence, note the fact that if is a solution of (3.12)–(3.14), then . Thus, we define It follows from (3.14) that . Now, satisfies (3.13) because It follows from (3.18), (3.20), and (3.21) that Thus, satisfies (3.12) and is a unique solution of Problem 1.
It follows from , and (3.21) that in (3.21) is in .
Since we have shown that Problem 1 is equivalent to (3.18)–(3.20), to show the lemma we only need to show that Problem 2, equivalent to (3.18)–(3.20) too.
If is a solution of (3.18)–(3.20), let . Then one can directly calculate that is a solution of (3.15)–(3.17) and .
On the other hand, if is a solution of (3.15)–(3.17), let where is the solution of the Cauchy problem Since , . By Theorem 2.4, and so .
Obviously, , and this shows that satisfies (3.20). satisfies (3.19) because Finally, This shows that satisfies (3.18). The proof is complete.
Note that, for a given , Theorem 2.4 shows the Cauchy problem (3.15) and (3.16) (or equivalently (3.28)) has a unique solution . Thus, (3.29) does define an operator . To show that Problem 2 (and so Problem 1) has a unique solution, we only need to show that (3.29) has a solution . That is, has a fixed point in . To this end, let Set . Now, we show that for small the operator in (3.29) is a contraction from into itself.
If , then, according to Theorem 2.4, the function determined by (3.15)-(3.16) and therefore by (3.28) belongs to . Note that , , and . It follows from Lemma 2.3, Theorem 2.4, and (3.29) that and where comes from Lemma 3.3. Noting that ad , we choose such that when one has So, . For , by (3.29) The function is a solution of the Cauchy problem Thus, by Lemma 3.3 Applying Lemma 3.3 to and , respectively, one gets If we choose so that when then
One sees that for such , the operator is a contraction from into itself and, therefore, has a unique fixed point in . Thus, we have shown.
Furthermore, we have the following.
For we can write the integral equation similar to (3.29), but this time its domain is . As the proof above, define the ball in ; then there exists a such that the operator is a contraction from into itself. So, (3.29) has a solution for the domain . This contradicts the definition of . We must have .
For the stability, we have the following.
Corollary 3.8. If Problem 1 has a solution in , then it has a unique one.
The research is supported by the NSF of China (no. 11071048).
- C. Y. Zhang, “Pseudo-almost-periodic solutions of some differential equations,” Journal of Mathematical Analysis and Applications, vol. 181, no. 1, pp. 62–76, 1994.
- C. Y. Zhang, “Integration of vector-valued pseudo-almost periodic functions,” Proceedings of the American Mathematical Society, vol. 121, no. 1, pp. 167–174, 1994.
- R. P. Agarwal, B. de Andrade, and C. Cuevas, “Weighted pseudo-almost periodic solutions of a class of semilinear fractional differential equations,” Nonlinear Analysis, vol. 11, no. 5, pp. 3532–3554, 2010.
- E. Ait Dads and O. Arino, “Exponential dichotomy and existence of pseudo almost-periodic solutions of some differential equations,” Nonlinear Analysis A, vol. 27, no. 4, pp. 369–386, 1996.
- E. Ait Dads and K. Ezzibi, “Positive pseudo almost periodic solutions for some nonlinear delay integrable equation,” J. Cybemetics, vol. 6, pp. 134–145, 1994.
- E. Ait Dads and K. Ezzinbi, “Pseudo almost periodic solutions of some delay differential equations,” Journal of Mathematical Analysis and Applications, vol. 201, no. 3, pp. 840–850, 1996.
- E. A. Dads and K. Ezzinbi, “Existence of positive pseudo-almost-periodic solution for some nonlinear infinite delay integral equations arising in epidemic problems,” Nonlinear Analysis A, vol. 41, pp. 1–13, 2000.
- E. Ait Dads, K. Ezzinbi, and O. Arino, “Pseudo almost periodic solutions for some differential equations in a Banach space,” Nonlinear Analysis A, vol. 28, no. 7, pp. 1141–1155, 1997.
- A. I. Alonso, J. Hong, and R. Obaya, “Almost periodic type solutions of differential equations with piecewise constant argument via almost periodic type sequences,” Applied Mathematics Letters, vol. 13, no. 2, pp. 131–137, 2000.
- A. I. Alonso, J. Hong, and R. Obaya, “Exponential dichotomy and trichotomy for difference equations,” Computers & Mathematics with Applications, vol. 38, no. 1, pp. 41–49, 1999.
- A. I. Alonso, J. Hong, and J. Rojo, “A class of ergodic solutions of differential equations with piecewise constant arguments,” Dynamic Systems and Applications, vol. 7, no. 4, pp. 561–574, 1998.
- B. Basit and C. Zhang, “New almost periodic type functions and solutions of differential equations,” Canadian Journal of Mathematics, vol. 48, no. 6, pp. 1138–1153, 1996.
- J. Hong and C. Núñez, “The almost periodic type difference equations,” Mathematical and Computer Modelling, vol. 28, no. 12, pp. 21–31, 1998.
- J. Hong and R. Obaya, “Ergodic type solutions of some differential equations,” in Differential Equations and Nonlinear Mechanics, vol. 528, pp. 135–152, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2001.
- J. Hong, R. Obaya, and A. S. Gil, “Exponential trichotomy and a class of ergodic solutions of differential equations with ergodic perturbations,” Applied Mathematics Letters, vol. 12, no. 1, pp. 7–13, 1999.
- J. Hong, R. Obaya, and A. M. Sanz, “Ergodic solutions via ergodic sequences,” Nonlinear Analysis A, vol. 40, pp. 265–277, 2000.
- J. Hong, R. Obaya, and A. Sanz, “Almost periodic type solutions of some differential equations with piecewise constant argument,” Nonlinear Analysis A, vol. 45, pp. 661–688, 2001.
- H.-X. Li, F.-I. Huang, and J.-Y. Li, “Composition of pseudo almost-periodic functions and semilinear differential equations,” Journal of Mathematical Analysis and Applications, vol. 255, no. 2, pp. 436–446, 2001.
- R. Yuan, “Pseudo-almost periodic solutions of second-order neutral delay differential equations with piecewise constant argument,” Nonlinear Analysis A, vol. 41, pp. 871–890, 2000.
- C. Zhang, Almost Periodic Type Functions and Ergodicity, Science Press, Beijing, China, 2003.
- C. Y. Zhang, “Pseudo almost periodic solutions of some differential equations. II,” Journal of Mathematical Analysis and Applications, vol. 192, no. 2, pp. 543–561, 1995.
- C. Zhang, “Vector-valued pseudo almost periodic functions,” Czechoslovak Mathematical Journal, no. 3, pp. 385–394, 1997.
- C.-Y. Zhang, “Ergodicity and its applications. I. Basic properties,” Acta Analysis Functionalis Applicata, vol. 1, no. 1, pp. 28–39, 1999.
- C.-Y. Zhang, “Ergodicity and its applications. II. Averaging method of some dynamical systems,” Acta Analysis Functionalis Applicata, vol. 1, no. 2, pp. 146–159, 1999.
- C. Zhang, “Ergodicity and its applications in regularity and solutions of pseudo-almost periodic equations,” Nonlinear Analysis A, vol. 46, no. 4, pp. 511–523, 2001.
- C. Zhang and H. Yao, “Converse problems of Fourier expansion and their applications,” Nonlinear Analysis A, vol. 56, no. 5, pp. 761–779, 2004.
- J. Bourgain, “Construction of approximative and almost periodic solutions of perturbed linear Schrödinger and wave equations,” Geometric and Functional Analysis, vol. 6, no. 2, pp. 201–230, 1996.
- C. Corduneanu, Almost Periodic Functions, Interscience Publishers, Chelsea, NY, USA, 1st edition, 1968.
- C. Corduneanu, Almost Periodic Functions, Interscience Publishers, Chelsea, NY, USA, 2nd edition, 1989.
- A. M. Fink, Almost Periodic Differential Equations, vol. 377 of Lecture Notes in Mathematics, Springer, Berlin, Germany, 1974.
- B. M. Levitan and V. V. Zhikov, Almost Periodic Functions and Differential Equations, Cambridge University Press, Cambridge, UK, 1982.
- W. Shen, “Traveling waves in time almost periodic structures governed by bistable nonlinearties, I stability and uniqueness; II. existence,” Journal of Differential Equations, vol. 159, no. 1, pp. 1–110, 1999.
- F. Yang and C. Zhang, “Slowly oscillating solutions of parabolic inverse problems,” Journal of Mathematical Analysis and Applications, vol. 335, no. 2, pp. 1238–1258, 2007.
- F. Yang and C. Zhang, “Slowly oscillating solutions of a parabolic inverse problem: boundary value problems,” Boundary Value Problems, vol. 2010, Article ID 471491, 12 pages, 2010.
- C. Zhang and F. Yang, “Remotely almost periodic solutions of parabolic inverse problems,” Nonlinear Analysis A, vol. 65, no. 8, pp. 1613–1623, 2006.
- C. Zhang and F. Yang, “Pseudo almost periodic solutions to parabolic boundary value inverse problems,” Science in China A, vol. 51, no. 7, pp. 1203–1214, 2008.
- A. Friedman, Partial Differential Equations of Parabolic Type, Prentice-Hall, Englewood Cliffs, NJ, USA, 1964.
- J. K. Hale and S. M. Verduyn Lunel, Introduction to Functional-Differential Equations, vol. 99 of Applied Mathematical Sciences, Springer, New York, NY, USA, 1993.
- B. Guo, Inverse Problem of Parabolic Partial Dfferential Equations, Science and Technology Press, Harbin, China, 1988.
- H. W. Engl, M. Hanke, and A. Neubauer, Rugularrization of Inverse Problems, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1996.