This paper presents an existence theorem of the solutions for a boundary value problem of fractional order differential equations with integral boundary conditions, by using measure of noncompactness combined with Mönch fixed point theorem. An example is furnished to illustrate the validity of our outcomes.
Quite recently, fractional differential equations become one of the most important research topic, since their applications in various applied science, as in physics, finance, hydrology, biophysics, thermodynamics, control theory, statistical mechanics, for example see [1,2]. many results were given concerning the existence and uniqueness of the solution of such equations by using various techniques, while the fixed point theory tool still one of the efficacy methods, see for example. Several authors tried to develop a technique that depends on the Darbo or the Monch fixed point theorems with the Hausdorff or Kuratowski measure of noncompactness.
This article deals with the existence of solutions for boundary value problems with fractional order differential equations and nonlinear integral boundary conditions. We furnish an example to illustrate our results.
Consider the following boundary value problems:\(f : [0; 1]\times C([0; 1];\mathbb{R})\times\mathbb{R} \longrightarrow R\), \(g \in C([0,1],\mathbb{R})\), \(a, b, \lambda \in \mathbb{R}_{+}\), \( a+b > 0\) and \(\frac{a}{a+b}< \alpha-1\).
Definition 1. [3,4] Let \(E\) be a Banach space and \(\Omega_E\) be the bounded subsets of \(E\). The Kuratowski measure of noncompactness is the map \(\alpha : \Omega_E\rightarrow [0,\infty]\) defined by \[\mu(B)=\liminf\{\epsilon>0:\,\, B\subseteq\cup_{i=1}^nB_i,\,\,diam(B_i)\leq\epsilon\},\,\,\,B\in\Omega_E,\] where \[diam(B_i ) = sup\{\|u – v\|_E : u, v \in B_i \}.\]
The Kuratowski measure of noncompactness satisfies the following properties;Lemma 1.[3,4] Let \(A\) and \(B\) bounded sets. Then
Definition 2. [5] The Riemann Liouville fractional integral of order \(q > 0\) of \(x :(0,\infty) \rightarrow\mathbb{R}\) is given by \[I^\alpha_{0^+}x(t)=\frac{1}{\Gamma(\alpha)}\displaystyle\int_{0}^{t}(t-s)^{\alpha-1}x(s)ds\] provided that the right hand side is defined on \((0,\infty)\).
Definition 3. [5] The Riemann Liouville fractional derivative of order \(q\in (0,1) 0\) of \(x :(0,\infty) \rightarrow\mathbb{R}\) is given by \[^{RL}D^\alpha_{0^+}x(t)=\frac{1}{\Gamma(n-q)}\displaystyle\frac{d^{(n)}}{dt}\int_{0}^{t}(t-s)^{n-q-1}x(s)ds,\;\ n=[q]+1,\] where \(\Gamma(q)\) denotes the classical gamma function, provided that the right-hand side is pointwise defined on \((0,\infty)\).
Definition 4.[5] The fractional derivative in Caputo sense of order \(q>0\) for a function \(x:(0,\infty)\rightarrow \mathbb{R}\) is given by \[^{c}D^{\alpha}x(t)=\frac{1}{\Gamma(n-q)}\int_{0}^{t}(t-s)^{n-q-1}x^{(n)}(s)ds,\] where \(n=[q]+1\), provided that the right side is pointwise defined on \((0,\infty)\).
Lemma 2.[5] Let \(\alpha > 0\), then the differential equation \[^{c}D^\alpha x(t)=0\] has solutions \(x(t) =\displaystyle\sum_{i=0}^{n-1} c_it^i, c_i \in \mathbb{R}, n = [\alpha]+1\).
Lemma 3.[5] Let \(\alpha > 0\), then \[\displaystyle I^{\alpha c}D^\alpha x(t) = x(t)-\sum_{i=0}^{n-1}c_it^i, c_i \in \mathbb{R}, n= [\alpha]+1.\]
Theorem 1. [1] Let \(X\) be a Banach space and \(0\in C\) be a nonempty, bounded, closed and convex subset of \(X\). Suppose a continuous mapping \(N : C \rightarrow C \) is such that for all non empty subsets V of C, \[\mu(N(V))\leq k\mu(V),\] where \(0 \leq k < 1\), and \(\mu\) is the Kuratowski measure of noncompactness, then \(N\) has a fixed point in \(C.\)
Theorem 2.[6] Let \(C\) be a bounded, closed and convex subset of a Banach space such that \(0\in C\), and let \(T\) be a continuous mapping of \(C\) into itself. If the implication \[V=\overline{conv}T(V)\,\,\,\,or\,\,\,\,V=T(V)\cup{0}\Rightarrow\mu(V)=0\] holds for every subset \(V\) of \(C\), then \(T\) has a fixed point.
Lemma 4.[7] Let \(D\) be a bounded, closed and convex subset of the Banach space \(C(J,X)\), \(G\) a continuous function on \(J\times J\) and \(f\) a function from \(J \times X \rightarrow X\) which satisfies the Carathéodory conditions, and suppose there exists \(p \in L^1(J,R_+)\) such that, for each \(t\in J\) and each bounded set \(B \subset X\), we have \[\displaystyle\lim_{h\rightarrow0^+}\mu\big(f\big(J_{t,h}\times B\big)\big)\leq p(t)\mu(B);\,\, here \,\,J_{t,h} = [t – h, t] \cap J.\] If \(V\) is an equicontinuous subset of \(D\), then \[\mu\big(\big\{\int_J G(s, t)f(s, x(s))ds: x \in V\big\}\big)\leq\int_J\parallel G(t, s)\parallel p(s)\mu(V (s))ds.\]
Lemma 5. Let \(X\) be a Banach space and \(F\subset C(J,X)\). If the following conditions are satisfied:
Lemma 6. Let \(1 < \alpha < 2\) and \( y \in C([0, 1])\). A function \(x\) is a solution of the fractional integral equation
Proof. By Lemma 3, we reduce (4) to an equivalent integral equation \[ x(t) =-\frac{1}{\Gamma(\alpha)} \int_{0}^{t}(t-s)^{\alpha-1}f(s) d s+c_{0}+c_{1} t ,\] \[ x^{\prime}(t) =-\frac{1}{\Gamma(\alpha-1)} \int_{0}^{t}(t-s)^{\alpha-2}f(s) ds+c_{1} ,\] for some constants \(c_0, c_1\in X\). Boundary conditions of (4) give \[ a c_{0}-b c_{1}=0,\] \[-\frac{1}{\Gamma(\alpha)} \int_{0}^{1}(1-s)^{\alpha-1}f(s) ds+c_{0}+c_{1}=\int_{0}^{1}g(s)ds+\lambda. \] Therefore \[\left\{\begin{array}{ll} c_{0}=\frac{b}{a+b}\left[\frac{1}{\Gamma(\alpha)} \int_{0}^{1}(1-s)^{\alpha-1}f(s) ds+\int_{0}^{1}g(s) ds+\lambda\right], \\ \\ c_{1}=\frac{a}{a+b}\left[\frac{1}{\Gamma(\alpha)} \int_{0}^{1}(1-s)^{\alpha-1} f(s) d s+\int_{0}^{1}f(s)ds+\lambda\right].&\end{array}\right.\] Thus \[ \begin{aligned} x(t)&=-\frac{1}{\Gamma(\alpha)} \int_{0}^{t}(t-s)^{\alpha-1}f(s) d s+\frac{b}{a+b}\left[\frac{1}{\Gamma(\alpha)} \int_{0}^{1}(1-s)^{\alpha-1}f(s) ds+\int_{0}^{1} h(s) y(s) d s+\lambda\right]\\ &\;\;\;\;\;+\frac{at}{a+b}\left[\frac{1}{\Gamma(\alpha)} \int_{0}^{1}(1-s)^{\alpha-1} k(s) d s+\int_{0}^{1} g(s)ds+\lambda\right] \\ &\;\;\;\;\;\times\int_{0}^{t}\left[ \frac{(a t+b)(1-s)^{\alpha-1}}{(a+b) \Gamma(\alpha)}-\frac{(t-s)^{\alpha-1}}{\Gamma(\alpha)}\right]f(s)ds+\int_{t}^{1} \frac{(a t+b)(1-s)^{\alpha-1}}{(a+b)\Gamma(\alpha)}f(s) ds\\ &\;\;\;\;\;+\frac{a t+b}{a+b} \int_{0}^{1}g(s) ds+\frac{a t+b}{a+b} \lambda\\ &=\int_{0}^{1} G(t, s)f(s) ds+\frac{a t+b}{a+b} \int_{0}^{1} g(s)d s+\frac{a t+b}{a+b} \lambda. \end{aligned} \] The proof is complete.
Since, we have
\[\int_{0}^{1}G(t,s)ds=\frac{1}{\Gamma(\alpha)}\Big(\int{0}^{t}(t-s)^{\alpha-1}ds+\frac{at+b}{a+b}\int{0}^{1}(1-s)^{\alpha-1}ds\Big)\] \[ \frac{1}{\Gamma(\alpha+1)}\big( t^{\alpha}+\frac{at+b}{a+b}\big)\leq\frac{2}{\Gamma(\alpha+1)}.\] Assume thatTheorem 3. Under the assumptions (A1)-(A5) the Problem (1) has a solution provided \[\frac{2K}{(1-L)\Gamma(\alpha+1)}+N< 1.\]
Proof. Transform the Problem (1) into a fixed point problem. Consider the operator \(T:X=C ([0,1],\mathbb{R})\longrightarrow C ([0,1],\mathbb{R})\) defined by \[ Tx(t)=\int_{0}^{1} G(t, s)f(t,x(s),^{c}D^{\alpha} x(s)) ds+\frac{at+b}{a+b} \int_{0}^{1}g(s,x(s))ds+\frac{a t+b}{a+b}\lambda. \]
Clearly, the fixed points of the operator \(T\) are solutions of the Problem (1). We shall show that \(T\) satisfies the assumptions of Theorem 3. The proof will be given in three steps.
Step 1: \(T\) is continuous. Let \((x_{n})\) be a sequence such that \(x_{n}\longrightarrow x\) in \(C ([0,1], X)\), then for each \(t\in[0,1]\) we have \[|T(x_{n})(t)-T(x)(t)| \leq| \int_{0}^{1}|G(t, s)f(t,x_{n}(t),^{c}D^{\alpha}x_{n}(t))-f(t,x(t),^{c}D^{\alpha}x(t)|ds\] \[ \;\;\;\;\;\;\;+\frac{a t+b}{a+b} \int_{0}^{1}( g(s,x_{n}(s))-g(s,x(s))|ds .\] By \((A1)\) and \((A3)\), we have \[ \begin{aligned} \left|f(t,x_{n}(t),^{c}D^{\alpha}x_{n}(t))-f(t,x(t),^{c}D^{\alpha}x(t)\right|& \leq K\left|x_{n}-x\right|+L\left|^{c}D^{\alpha}x_{n}(t)-^{c}D^{\alpha}x(t)\right|\\ & \leq K|x_{n}-x|+L|f(t, x_{x}(t),^{c}D^{\alpha } x_{n} ( t ))-f(t, x(t), ^{c}D^{\alpha} x ( t ))|. \end{aligned} \] Then \[ |f(t,x_{n}(t),^{c}D^{\alpha}x_{n}(t))-f(t,x(t),^{c}D^{\alpha}x(t)|\leq\frac{K}{1-L}|x_{n}-x|,\] and \[|g_{t},x_n(t)-g(t,x(t))|\leq N|x_{n}-x|. \] So \[ \begin{aligned} |T(x_{n})(t)-T(x)(t)| & \leq\Big(\frac{2K}{1-L} +N\Big)\|x_{n}-x|.\end{aligned} \] Since \(x_{n} \longrightarrow x\), for each \(t \in [0,1]\). \[|T(x_{n}(t)-T(x)(t))| \longrightarrow 0, \qquad when \quad n \longrightarrow \infty.\] So \[\|T\left(x_{n}\right)(t)-T(x)(t)\| \rightarrow 0,\,\,\, when \,\,\, n \rightarrow \infty.\] Therefore, \( T \) is continuous. Now, let \[r\geq \frac{1}{(1-L)\Gamma(\alpha+1)}( K r+f_0)+N r + g_{0}+\lambda \] where \[ f_0=\displaystyle\sup _{t \in [0,1]}\|f(t, 0,0)\|, \;\ g_{0}=\displaystyle\sup _{t \in [0,1]}\|g(t, 0)\|. \]Define \(B_{r} = \lbrace x \in X:\Vert x\Vert \leq r \rbrace\). It is clear that \( B_ {r} \) is a bounded, closed and convex subset of \(X\).
Step 2: \(T\) maps \(B_{r}\) into itself, i.e., \(T (B_{r}) \subseteq B_{r}\). Let \( x \in B_{r}\), so for each \(t \in [0,1]\), we have \[ \begin{aligned} |T(x)(t)|&= \Big|\int_{0}^{1}G(t,s)f(t,x_{n}(t),^{c}D^{\alpha}x(t))ds+\frac{at+b}{a+b} \int_{0}^{1}g(s,x(s))ds+\frac{at+b}{a+b} \lambda\Big|\\ & \leq\int_{0}^{1}G(t,s)f(t,x_{n}(t),^{c}D^{\alpha}x_{n}(t))ds+ \frac{at+b}{a+b}\int_{0}^{1}\int_{0}^{1}g(s,x(s)) ds+\frac{at+b}{a+b}\lambda \\ & \leq \frac{2}{\Gamma(\alpha+1)}\|f(s,x(s),^{c}D^{\alpha}x(t))\|+\|g(s,x(s))\|+\lambda.\end{aligned}\] By \((A1)\) et \((A3)\), we have for each \(t \in [0,1]\)Finally, we present a numerical example to illustrate our results.
Example 1. Let us consider the following fractional boundary value problem: