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Existence and uniqueness of solutions for nonlinear impulsive differential equations with twopoint and integral boundary conditions
Advances in Difference Equations volume 2013, Article number: 173 (2013)
Abstract
In the present paper, a system of nonlinear impulsive differential equations with twopoint and integral boundary conditions is investigated. Theorems on the existence and uniqueness of a solution are established under some sufficient conditions on nonlinear terms. A simple example of application of the main result of this paper is presented.
1 Introduction
The theory of impulsive differential equations is an important branch of differential equations which has an extensive physical background. Impulsive differential equations arise frequently in the modeling of many physical systems whose states are subject to sudden change at certain moments. There has been a significant development in impulsive theory especially in the area of impulsive differential equations with fixed moments (see, for instance, the monographs [1–4] and the references therein).
Many of the physical systems can better be described by integral boundary conditions. Integral boundary conditions are encountered in various applications such as population dynamics, blood flow models, chemical engineering and cellular systems. Moreover, boundary value problems with integral conditions constitute a very interesting and important class of problems. They include twopoint, threepoint, multipoint and nonlocal boundary value problems as special cases. For boundary value problems with nonlocal boundary conditions and comments on their importance, we refer the reader to the papers [5–18] and the references therein.
In the present paper, we study the existence and uniqueness of the system of nonlinear impulsive differential equations of the type
subject to twopoint and integral boundary conditions
and impulsive conditions
where A,B\in {R}^{n\times n} are given matrices and det(A+B)\ne 0; f,g:[0,T]\times {R}^{n}\to {R}^{n} and {I}_{i}:{R}^{n}\to {R}^{n} are given functions;
where
are the right and lefthand limits of x(t) at t={t}_{i}, respectively.
The organization of the present paper is as follows. First, we provide the necessary background. Second, theorems on the existence and uniqueness of a solution of problem (1), (2), (3) are established under some sufficient conditions on the nonlinear terms. Third, a simple example of application of the main result of this paper is presented.
2 Preliminaries
In this section, we present some basic definitions and preliminary facts which are used throughout the paper. By C([0,T],{R}^{n}), we denote the Banach space of all vector continuous functions x(t) from [0,T] into {R}^{n} with the norm
where \cdot  is the norm in the space {R}^{n}.
We consider the linear space
PC([0,T],{R}^{n}) is a Banach space with the norm
We define a solution of problem (1), (2) and (3) as follows.
Definition 2.1 A function x\in PC([0,T],{R}^{n}) is said to be a solution of problem (1), (2) and (3) if
for each t\in [0,T], t\ne {t}_{i}, i=1,2,\dots ,p, and for each
and boundary condition (2) are satisfied.
Lemma 2.1 Let y,g\in C([0,T],{R}^{n}) and {a}_{i}\in {R}^{n}, i=1,2,\dots ,p. Then the boundary value problem for the impulsive differential equation
has a unique solution x(t)\in PC([0,T],{R}^{n}) given by
for t\in ({t}_{i},{t}_{i+1}], i=0,1,\dots ,p, where
Proof Assume that x(t) is a solution of boundary value problem (4)(6), then integrating equation (4) for t\in (0,{t}_{j+1}), we get
Using this formula and condition (5), we can write
Applying formula (7) and condition (6), we get
Hence, we obtain
From formulas (7) and (9), it follows
Therefore we can state that
Lemma 2.1 is established. □
Remark 2.1 Note that for solution (7) we have that:

i.
C={(A+B)}^{1}{\int}_{0}^{T}g(s)\phantom{\rule{0.2em}{0ex}}ds is the solution of \dot{x}(t)=0 with nonlocal boundary condition (6);

ii.
The function {\int}_{0}^{T}K(t,\tau )y(\tau )\phantom{\rule{0.2em}{0ex}}d\tau is the solution of \dot{x}(t)=y(t) with the nonlocal boundary condition Ax(0)+Bx(T)=0. Here K(t,\tau ) is Green’s function of this problem;

iii.
The functions {\sum}_{0<{t}_{k}<T}K({t}_{i},{t}_{k}){a}_{k}, i=1,2,\dots ,p, are the solution of \dot{x}(t)=0 with the nonlocal boundary condition Ax(0)+Bx(T)=0 and are jumps (5).
Lemma 2.2 Assume that f,g\in C([0,T]\times {R}^{n},{R}^{n}) and {I}_{k}(x)\in C({R}^{n}), then the function x(t) is a solution of impulsive boundary value problem (1), (2) and (3) if and only if x(t) is a solution of the impulsive integral equation
for t\in ({t}_{i},{t}_{i+1}], i=0,1,\dots ,p.
Proof Let x(t) be a solution of boundary value problem (1), (2) and (3), then in the same way as in Lemma 2.1, we can prove that it is a solution of impulsive integral equation (11). By direct verification we can show that the solution of impulsive integral equation (11) also satisfies equation (1) and nonlocal boundary condition (3). Also, it is easy to verify that it satisfies condition (2). Lemma 2.2 is proved. □
3 Main results
The first main statement of the present study is the existence and uniqueness of boundary value problem (1), (2) and (3), a result that is based on a Banach fixed point theorem.
Theorem 3.1 Assume that:
(H1) There exists a constant N>0 such that
for any t\in [0,T] and all x,y\in {R}^{n}.
(H2) There exists a constant M>0 such that
for any t\in [0,T] and all x,y\in {R}^{n}.
(H3) There exist constants {l}_{i}>0, i=1,2,\dots ,p, such that
for all x,y\in {R}^{n}.
If
then boundary value problem (1), (2) and (3) has a unique solution on [0,T]. Here
Proof We will transform problem (1), (2) and (3) into a fixed point problem. Consider the operator
defined by
for t\in ({t}_{i},{t}_{i+1}], i=0,1,\dots ,p.
Clearly, the fixed points of the operator F are solutions of problem (1), (2) and (3). We will use the Banach contraction principle to prove that F defined by (13) has a fixed point. We will show that F is a contraction.
Let x,y\in PC([0,T],{R}^{n}). Then, for each t\in ({t}_{i},{t}_{i+1}], we have that
Thus
Consequently, by assumption (12) the operator F is a contraction. As a consequence of the Banach fixed point theorem, we deduce that the operator F has a fixed point which is a solution of problem (1), (2) and (3). Theorem 3.1 is established. □
The second main statement of the present study is an existence result for boundary value problem (1), (2) and (3) that is based on the Schaefer fixed point theorem.
Theorem 3.2 Assume that:
(H4) The function f:[0,T]\times {R}^{n}\to {R}^{n} is continuous.
(H5) There exists a constant {N}_{1}>0 such that
(H6) The function g:[0,T]\times {R}^{n}\to {R}^{n} is continuous.
(H7) There exists a constant {N}_{2}>0 such that
(H8) The functions {I}_{k}(x), x\in {R}^{n}, k=1,2,\dots ,p, are continuous and there exists a constant {N}_{3}>0 such that
for all x\in {R}^{n}.
Then boundary value problem (1), (2) and (3) has at least one solution on [0,T].
Proof We will divide the proof into four main steps in which we will show that under the assumptions of the theorem, the operator F has a fixed point.
Step 1. The operator F under the assumptions of the theorem is continuous. Let \{{x}_{n}\} be a sequence such that {x}_{n}\to x in PC([0,T],{R}^{n}). Then, for any t\in ({t}_{i},{t}_{i+1}], i=0,1,\dots ,p,
Since f, g and {I}_{k}, k=1,2,\dots ,p, are continuous functions, we have
as n\to \mathrm{\infty}.
Step 2. The operator F maps bounded sets in bounded sets in PC([0,T],{R}^{n}). Indeed, it is enough to show that for any \eta >0, there exists a positive constant l such that for any x\in {B}_{\eta}=\{x\in PC([0,T],{R}^{n}):\parallel x\parallel \le \eta \}, we have \parallel F(x(\cdot ))\parallel \le l. Applying the triangle inequality, assumptions (H5), (H7) and (H8), for t\in ({t}_{i},{t}_{i+1}], we obtain
for any t\in [0,T]. Hence,
Thus
Step 3. The operator F maps bounded sets into equicontinuous sets of PC([0,T],{R}^{n}).
Let {\tau}_{1},{\tau}_{2}\in ({t}_{i},{t}_{i+1}], {\tau}_{1}<{\tau}_{2}, {B}_{\eta} be a bounded set of PC([0,T],{R}^{n}) as in Step 2, and let x\in {B}_{\eta}. We have that
Then, applying the triangle inequality, assumptions (H5), (H7) and (H8), we obtain
As {\tau}_{1}\to {\tau}_{2}, the righthand side of the above inequality tends to zero. As a consequence of Steps 1 to 3 together with the ArzelaAscoli theorem, we can conclude that the operator F:PC([0,T],{R}^{n})\to PC([0,T],{R}^{n}) is completely continuous.
Step 4. A priori bounds. Now, it remains to show that the set
is bounded. Let x=\lambda (Fx) for some 0<\lambda <1. Then, for any t\in ({t}_{i},{t}_{i+1}], i=0,1,\dots ,p, we have
This implies by (H5), (H7) and (H8) (as in Step 2) that for any t\in [0,T], we have
Therefore, for every t\in [0,T], we have that
This shows that the set Δ is bounded. As a consequence of the Schaefer fixed point theorem, we deduce that F has a fixed point which is a solution of problem (1), (2) and (3). Theorem 3.2 is established. □
In the following theorem, we give an existence result for problem (1), (2) and (3) by means of an application of a LeraySchauder type nonlinear alternative, where the conditions (H5), (H7) and (H8) are weakened.
Theorem 3.3 Assume that (H4), (H6) and the following conditions hold:
(H9) There exist {\theta}_{f}\in {L}^{1}([0,T],{R}^{+}) and a continuous and nondecreasing {\psi}_{f}:[0,\mathrm{\infty})\to [0,\mathrm{\infty}) such that
(H10) There exist {\theta}_{g}\in {L}^{1}([0,T],{R}^{+}) and a continuous nondecreasing {\psi}_{g}:[0,\mathrm{\infty})\to [0,\mathrm{\infty}) such that
(H11) There exist \psi :[0,\mathrm{\infty})\to [0,\mathrm{\infty}) and a continuous and nondecreasing function such that
for all x\in {R}^{n}.
(H12) There exists a number K>0 such that
Then boundary value problem (1), (2) and (3) has at least one solution on [0,T].
Proof Consider the operator F defined in Theorems 3.2 and 3.3. It can be easily shown that F is continuous and completely continuous. For \lambda \in [0,1] let x be such that for each t\in ({t}_{i},{t}_{i+1}], i=0,1,\dots ,p, we have x(t)=\lambda (Fx)(t). Then from (H9)(H11) we have
for each t\in ({t}_{i},{t}_{i+1}], i=0,1,\dots ,p. Therefore,
Then, by condition (H12), there exists K such that \parallel x\parallel \ne K.
Let
The operator F:\overline{U}\to PC([0,T],R) is continuous and completely continuous. By the choice of U, there exists no x\in \partial U such that x=\lambda F(x) for some \lambda \in (0,1). As a consequence of the nonlinear alternative of LeraySchauder type [19], we deduce that F has a fixed point x in \overline{U}, which is a solution of problem (1), (2) and (3). Theorem 3.2 is proved. □
4 An example
Now, we give an example to illustrate the usefulness of our main results. Let us consider the following nonlocal boundary value problem for a system of impulsive differential equations:
Evidently, T=p=1, A+B=E, \parallel {(A+B)}^{1}\parallel =1 and S=1. Hence, the conditions (H1)(H2) hold with N=M=0.2; {l}_{1}=0.1. We can easily see that condition (4) is satisfied. Indeed,
then by Theorem 3.1 boundary value problem (14) has a unique solution on [0,1].
5 Conclusion
In this work, some existence and uniqueness of a solution results have been established for the system of nonlinear impulsive differential equations with twopoint and integral boundary conditions under some sufficient conditions on the nonlinear terms. These statements without proof are formulated in [20]. Of course, such type of existence and uniqueness results hold under the same sufficient conditions on the nonlinear terms for the system of nonlinear impulsive differential equations (1), subject to multipoint nonlocal and integral boundary conditions
and impulsive conditions
where {B}_{j}\in {R}^{n\times n} are given matrices and {\sum}_{j=1}^{J}\parallel {B}_{j}\parallel <1. Here, 0<{\lambda}_{1}<\cdots <{\lambda}_{J} ≤T.
Moreover, applying the result of the paper [21], the singlestep difference schemes for the numerical solution of nonlocal boundary value problem (1), (16) and (17) can be presented. Of course, such type of existence and uniqueness results hold under some sufficient conditions on the nonlinear terms for the solution of the system of these difference schemes.
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Ashyralyev, A., Sharifov, Y.A. Existence and uniqueness of solutions for nonlinear impulsive differential equations with twopoint and integral boundary conditions. Adv Differ Equ 2013, 173 (2013). https://doi.org/10.1186/168718472013173
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DOI: https://doi.org/10.1186/168718472013173
Keywords
 Nonlinear Term
 Fixed Point Theorem
 Triangle Inequality
 Nonlocal Boundary
 Impulsive Differential Equation