Electronic Journal of Differential Equations, Vol. 2013 (2013), No. 60, pp. 1–10. ISSN: 1072-6691. URL: http://ejde.math.txstate.edu or http://ejde.math.unt.edu ftp ejde.math.txstate.edu INTEGRO-DIFFERENTIAL EQUATIONS OF FRACTIONAL ORDER WITH NONLOCAL FRACTIONAL BOUNDARY CONDITIONS ASSOCIATED WITH FINANCIAL ASSET MODEL BASHIR AHMAD, SOTIRIS K. NTOUYAS Abstract. In this article, we discuss the existence of solutions for a boundaryvalue problem of integro-differential equations of fractional order with nonlocal fractional boundary conditions by means of some standard tools of fixed point theory. Our problem describes a more general form of fractional stochastic dynamic model for financial asset. An illustrative example is also presented. 1. Formulation and basic result Fractional calculus, regarded as a branch of mathematical analysis dealing with derivatives and integrals of arbitrary order, has been extensively developed and applied to a variety of problems appearing in sciences and engineering. It is worthwhile to mention that this branch of mathematics has played a crucial role in exploring various characteristics of engineering materials such as viscoelastic polymers, foams, gels, and animal tissues, and their engineering and scientific applications. For a recent detailed survey of the activities involving fractional calculus, we refer a recent paper by Machado, Kiryakova and Mainardi [16]. Some recent work on the topic can be found in [1, 2, 3, 4, 5, 6, 7, 9, 10, 13, 14, 17] and references therein. The underlying dynamics of equity prices following a jump process or a Levy process provide a basis for modeling of financial assets. The CGMY, KoBoL and FMLS are examples of some interesting financial models involving the dynamics of stock prices. In [8], it is shown that the prices of financial derivatives are expressible in terms of fractional derivative. In [15], the author described the dynamics of a financial asset by the fractional stochastic differential equation of order µ (representing the dynamical memory effects in the market stochastic evolution) with fractional boundary conditions. In the present paper, we study a more general model associated with financial asset. 2000 Mathematics Subject Classification. 34A08, 34B10, 34B15. Key words and phrases. Fractional differential equations; integral boundary conditions; existence; fixed point theorems; financial asset. c 2013 Texas State University - San Marcos. Submitted December 6, 2012. Published February 26, 2013. 1 2 B. AHMAD, S. K. NTOUYAS EJDE-2013/60 Precisely, we consider the following problem: −Dα x(t) = Af (t, x(t)) + BI β g(t, x(t)), Dδ x(0) = 0, (n − 1) < α ≤ n, t ∈ [0, 1], Z η Dδ x(s)ds, Dδ+1 x(0) = 0, . . . , Dδ+(n−2) x(0) = 0, Dδ x(1) = 0 (1.1) where 0 < δ ≤ 1, α − δ > n, 0 < β < 1, 0 < η < 1, D(·) denotes the RiemannLioville fractional derivative of order (·), f, g are given continuous function, and A, B are real constants. We remark that the problem (1.1) also arises in real estate asset securitization modeling [18]. By the substitution x(t) = I δ y(t) = D−α y(t), the problem (1.1) takes the form −Dα−δ y(t) = Af (t, I δ y(t)) + BI β g(t, I δ y(t)), y(0) = 0, y 0 (0) = 0, . . . , y (n−2) (0) = 0, t ∈ [0, 1], Z η y(1) = y(s)ds. (1.2) 0 Lemma 1.1. For any h ∈ C(0, 1) ∩ L(0, 1), the unique solution of the linear fractional boundary-value problem −Dα−δ y(t) = h(t), y(0) = 0, t ∈ [0, 1], y 0 (0) = 0, . . . , y (n−2) (0) = 0, Z y(1) = η y(s)ds, (1.3) 0 is y(t) = −I α−δ h(t) + (α − δ)tα−δ−1 α−δ I h(1) − I α−δ+1 h(η) , α−δ α−δ−η where I (·) (·) denotes Riemann-Liouville integral. Proof. It is well known that the solutions of fractional differential equation in (1.1) can be written as y(t) = −I α−δ h(t) + c1 tα−δ−1 + c2 tα−δ−2 + c3 tα−δ−3 + · · · + cn tα−δ−n , (1.4) where c1 , c2 , . . . , cn ∈ R are arbitrary constants [12]. Using the given boundary conditions, we find that c2 = 0, c3 = 0, . . . , cn = 0 and α−δ α−δ α−δ+1 c1 = I h(1) − I h(η) . α − δ − η α−δ Substituting these values in (1.1) yields y(t) = −I α−δ h(t) + This completes the proof. (α − δ)tα−δ−1 α−δ α−δ+1 I h(1) − I h(η) . α − δ − η α−δ Thus, the solution of the linear variant of the problem (1.1) can be written as x(t) = I δ y(t) h i (α − δ)tα−δ−1 α−δ α−δ+1 I h(1) − I h(η) = I δ − I α−δ h(t) + α − δ − η α−δ Z t (t − s)δ−1 (α − δ) α−δ α α−δ+1 = −I h(t) + I h(1) − I h(η) sα−δ−1 ds α − δ − η α−δ Γ(δ) 0 EJDE-2013/60 NONLOCAL FRACTIONAL BOUNDARY-VALUE PROBLEMS 3 (α − δ) α−δ α−δ+1 = −I α h(t) + I h(1) − I h(η) × α − δ − η α−δ n tα−1 Z 1 o × (1 − ν)δ−1 ν α−δ−1 dν , Γ(δ) 0 where we have used the substitution s = νt in the integral of the last term. Using the relation for Beta function B(·, ·): Z 1 Γ(α)Γ(β + 1) , B(β + 1, α) = (1 − u)α−1 uβ du = Γ(α + β + 1) 0 we obtain x(t) = −I α h(t) + Γ(α − δ + 1)tα−1 α−δ α−δ+1 I h(1) − I h(η) . (α − δ − η α−δ )Γ(α) (1.5) The solution of the original nonlinear problem (1.1) can be obtained by replacing h with the right hand side of the fractional equation of (1.1) in (1.5). Let C = C([0, 1], R) denote the Banach space of all continuous functions from [0, 1] → R endowed with the norm defined by kxk = sup{|x(t)|, t ∈ [0, 1]}. In relation to problem (1.1), we define an operator U : C → C as (Ux)(t) Z = −A t Z t (t − s)α−1 (t − s)α+β−1 f (s, x(s))ds − B g(s, x(s))ds Γ(α) Γ(α + β) 0 0 Z 1 h Z 1 (1 − s)α−δ−1 (1 − s)α−δ+β−1 f (s, x(s))ds + B g(s, x(s))ds + Qtα−1 A Γ(α − δ) Γ(α − δ + β) 0 0 Z η Z η i (η − s)α−δ (η − s)α−δ+β −A f (s, x(s))ds − B g(s, x(s))ds , 0 Γ(α − δ + 1) 0 Γ(α − δ + β + 1) where Q= Γ(α − δ + 1) , (α − δ − η α−δ )Γ(α) α 6= δ + η α−δ . For the sake of convenience, we set n h tα η α−δ+1 i 1 Ω = sup |A| + |Q|tα−1 + Γ(α + 1) Γ(α − δ + 1) Γ(α − δ + 2) t∈[0,1] h io α+β t 1 η α−δ+β+1 + |B| + |Q|tα−1 + . Γ(α + β + 1) Γ(α − δ + β + 1) Γ(α − δ + β + 2) (1.6) 1.1. Existence results via Banach’s fixed point theorem. Theorem 1.2. Assume that f, g : [0, 1]×R → R are continuous functions satisfying the condition: (A1) |f (t, x) − f (t, y)| ≤ L1 |x − y|, |g(t, x) − g(t, y)| ≤ L2 |x − y|, for all t ∈ [0, 1], L1 , L2 > 0, x, y ∈ R. Then the boundary-value problem (1.1) has a unique solution if L < 1/Ω, where L = max{L1 , L2 } and Ω is given by (1.6). 4 B. AHMAD, S. K. NTOUYAS EJDE-2013/60 Proof. Let us define M = max{M1 , M2 }, where M1 , M2 are finite numbers given by ΩM supt∈[0,1] |f (t, 0)| = M1 , supt∈[0,1] |g(t, 0)| = M2 . Selecting r ≥ 1−LΩ , we show that UBr ⊂ Br , where Br = {x ∈ C : kxk ≤ r}. Using that |f (s, x(s)) ≤ |f (s, x(s)) − f (s, 0)|+|f (s, 0)| ≤ L1 r+M1 , |g(s, x(s))| ≤ |g(s, x(s))−g(s, 0)|+|g(s, 0)| ≤ L2 r+M2 for x ∈ Br and (1.6), it can easily be shown that k(Ux)k 1 η α−δ+1 i tα + |Q|tα−1 + Γ(α + 1) Γ(α − δ + 1) Γ(α − δ + 2) t∈[0,1] h io α+β η α−δ+β+1 t 1 + |B| + |Q|tα−1 + Γ(α + β + 1) Γ(α − δ + β + 1) Γ(α − δ + β + 2) = (Lr + M )Ω ≤ r, ≤ (Lr + M ) sup n h |A| which implies that UBr ⊂ Br . Now, for x, y ∈ C we obtain kUx − Uyk n Z ≤ sup |A| t∈[0,1] 0 t (t − s)α−1 |f (s, x(s)) − f (s, y(s))|ds Γ(α) t (t − s)α+β−1 |g(s, x(s)) − g(s, y(s))|ds Γ(α + β) 0 h Z 1 (1 − s)α−δ−1 α−1 + |Q|t |A| |f (s, x(s)) − f (s, y(s))|ds Γ(α − δ) 0 Z 1 (1 − s)α−δ+β−1 + |B| |g(s, x(s)) − g(s, y(s))|ds Γ(α − δ + β) 0 Z η (η − s)α−δ + |A| |f (s, x(s)) − f (s, y(s))|ds 0 Γ(α − δ + 1) Z η io (η − s)α−δ+β + |B| |g(s, x(s)) − g(s, y(s))|ds 0 Γ(α − δ + β + 1) n h tα η α−δ+1 i 1 ≤ L sup |A| + |Q|tα−1 + Γ(α + 1) Γ(α − δ + 1) Γ(α − δ + 2) t∈[0,1] h io α+β t η α−δ+β+1 1 + |B| + |Q|tα−1 + Γ(α + β + 1) Γ(α − δ + β + 1) Γ(α − δ + β + 2) × kx − yk Z + |B| = LΩkx − yk. By the given assumption, L < 1/Ω. Therefore U is a contraction. Thus, the conclusion of the theorem follows by the contraction mapping principle (Banach fixed point theorem). Now we present another variant of existence-uniqueness result. This result is based on the Hölder’s inequality. Theorem 1.3. Suppose that the continuous functions f and g satisfy the following assumptions: (H1) |f (t, x) − f (t, y)| ≤ m(t)|x − y|, |g(t, x) − g(t, y)| ≤ n(t)|x − y|, for t ∈ [0, 1], 1 x, y ∈ R, and m, n ∈ L γ ([0, 1], R+ ), γ ∈ (0, α − δ − n). EJDE-2013/60 NONLOCAL FRACTIONAL BOUNDARY-VALUE PROBLEMS 5 (H2) |A|kmkZ1 + |B|knkZ2 < 1, where 1 1 − γ 1−γ |Q| 1 − γ 1−γ Z1 = + Γ(α) α − γ Γ(α − δ) α − δ − γ 1−γ |Q| 1−γ + η α−δ+1−γ , Γ(α − δ + 1) α − δ + 1 − γ 1 − γ 1−γ 1−γ 1 1−γ |Q| + Γ(α + β) α + β − γ Γ(α − δ + β) α − δ + β − γ 1−γ 1−γ |Q| η α−δ+β+1−γ , + Γ(α − δ + β + 1) α − δ + β + 1 − γ γ R1 1 and kµk = 0 |µ(s)| γ ds , µ = m, n. Then the boundary value problem (1.1) has a unique solution. Z2 = Proof. For x, y ∈ R and for each t ∈ [0, 1], by Hölder inequality, we have kUx − Uyk n Z ≤ sup |A| t∈[0,1] 0 t t (t − s)α−1 m(s)|x(s) − y(s)|ds Γ(α) (t − s)α+β−1 n(s)|x(s) − y(s)|ds Γ(α + β) 0 h Z 1 (1 − s)α−δ−1 + |Q| |A| m(s)|x(s) − y(s)|ds Γ(α − δ) 0 Z 1 (1 − s)α−δ+β−1 + |B| n(s)|x(s) − y(s)|ds Γ(α − δ + β) 0 Z η (η − s)α−δ + |A| m(s)|x(s) − y(s)|ds 0 Γ(α − δ + 1) Z η io (η − s)α−δ+β + |B| n(s)|x(s) − y(s)|ds 0 Γ(α − δ + β + 1) n |A|kmk 1 − γ 1−γ |B|knk 1 − γ 1−γ α+β−γ ≤ sup tα−γ + t Γ(α) α − γ Γ(α + β) α + β − γ t∈[0,1] h |A|kmk 1 − γ 1−γ 1−γ |B|knk 1−γ + |Q| + Γ(α − δ) α − δ − γ Γ(α − δ + β) α − δ + β − γ 1−γ |A|kmk 1−γ + η α−δ+1−γ Γ(α − δ + 1) α − δ + 1 − γ 1−γ io |B|knk 1−γ + η α−δ+β+1−γ kx − yk Γ(α − δ + β + 1) α − δ + β + 1 − γ h 1 1 − γ 1−γ |Q| 1 − γ 1−γ ≤ |A|kmk + Γ(α) α − γ Γ(α − δ) α − δ − γ 1−γ i |Q| 1−γ + kx − yk Γ(α − δ + 1) α − δ + 1 − γ h 1 − γ 1−γ 1−γ 1 |Q| 1−γ + + |B|knk Γ(α + β) α + β − γ Γ(α − δ + β) α − δ + β − γ Z + |B| 6 B. AHMAD, S. K. NTOUYAS EJDE-2013/60 i 1−γ |Q| 1−γ η α−δ+β+1−γ kx − yk Γ(α − δ + β + 1) α − δ + β + 1 − γ = [|A|kmkZ1 + |B|knkZ2 ]kx − yk. + In view of condition (H2), it follows that U is a contraction mapping. Hence, Banach’s fixed point theorem applies and U has a unique fixed point which is the unique solution of problem (1.1). This completes the proof. 1.2. Existence result via Leray-Schauder Alternative. Lemma 1.4 (Nonlinear alternative for single valued maps [11]). Let E be a Banach space, C a closed, convex subset of E, U an open subset of C and 0 ∈ U . Suppose that F : U → C is a continuous, compact (that is, F (U ) is a relatively compact subset of C) map. Then either (i) F has a fixed point in U , or (ii) there is a u ∈ ∂U (the boundary of U in C) and λ ∈ (0, 1) with u = λF (u). Theorem 1.5. Assume that f, g : [0, 1]×R → R are continuous functions. Assume that: (A3) There exist functions p1 , p2 ∈ L1 ([0, 1], R+ ), and nondecreasing functions ψ1 , ψ2 : R+ → R+ such that |f (t, x)| ≤ p1 (t)ψ1 (kxk), |g(t, x)| ≤ p2 (t)ψ2 (kxk), for all (t, x) ∈ [0, 1] × R. (A4) There exists a constant M > 0 such that M > 1, |A|Λ1 ψ1 (M )kp1 kL1 + |B|Λ1 ψ2 (M )kp2 kL1 where 1 |Q| |Q| + + , Γ(α + 1) Γ(α − δ + 1) Γ(α − δ + 2) |Q| |Q| 1 + + . Λ2 = Γ(α + β + 1) Γ(α − δ + β + 1) Γ(α − δ + β + 2) Λ1 = Then the boundary-value problem (1.1) has at least one solution on [0, 1]. Proof. Consider the operator U : C → C with x = Ux, where (Ux)(t) Z = −A t Z t (t − s)α−1 (t − s)α+β−1 f (s, x(s))ds − B g(s, x(s))ds Γ(α) Γ(α + β) 0 0 Z 1 h Z 1 (1 − s)α−δ−1 (1 − s)α−δ+β−1 α−1 + Qt A f (s, x(s))ds + B g(s, x(s))ds Γ(α − δ) Γ(α − δ + β) 0 0 Z Z η η i (η − s)α−δ (η − s)α−δ+β −A f (s, x(s))ds − B g(s, x(s))ds . 0 Γ(α − δ + 1) 0 Γ(α − δ + β + 1) We show that F maps bounded sets into bounded sets in C([0, 1], R). For a positive number r, let Br = {x ∈ C([0, 1], R) : kxk ≤ r} be a bounded set in C([0, 1], R). Then |(Ux)(t)| EJDE-2013/60 NONLOCAL FRACTIONAL BOUNDARY-VALUE PROBLEMS 7 Z t (t − s)α−1 (t − s)α+β−1 p1 (s)ψ1 (kxk)ds + |B| p2 (s)ψ2 (kxk)ds Γ(α) Γ(α + β) 0 0 h Z 1 (1 − s)α−δ−1 α−1 |A| + |Q|t p1 (s)ψ1 (kxk)ds Γ(α − δ) 0 Z 1 (1 − s)α−δ+β−1 + |B| p2 (s)ψ2 (kxk)ds Γ(α − δ + β) 0 Z η (η − s)α−δ p1 (s)ψ1 (kxk)ds + |A| 0 Γ(α − δ + 1) Z η i (η − s)α−δ+β + |B| p2 (s)ψ2 (kxk)ds 0 Γ(α − δ + β + 1) o n |Q| |Q| 1 + + ≤ |A|ψ1 (r)kp1 kL1 Γ(α + 1) Γ(α − δ + 1) Γ(α − δ + 2) n o 1 |Q| |Q| + |B|ψ2 (r)kp2 kL1 + + . Γ(α + β + 1) Γ(α − δ + β + 1) Γ(α − δ + β + 2) Z t ≤ |A| Consequently kUxk o 1 |Q| |Q| + + Γ(α + 1) Γ(α − δ + 1) Γ(α − δ + 2) n o 1 |Q| |Q| + |B|ψ2 (r)kp2 kL1 + + . Γ(α + β + 1) Γ(α − δ + β + 1) Γ(α − δ + β + 2) ≤ |A|ψ1 (r)kp1 kL1 n Next we show that F maps bounded sets into equicontinuous sets of C([0, 1], R). Let t1 , t2 ∈ [0, 1] with t1 < t2 and x ∈ Br , where Br is a bounded set of C([0, 1], R). Then we obtain k(Ux)(t2 ) − (Ux)(t1 )k |A| Z t1 ≤ [(t2 − s)α−1 − (t1 − s)α−1 ]f (s, x(s))ds Γ(α) 0 Z t2 |A| + (t2 − s)α−1 f (s, x(s))ds Γ(α) t1 Z t1 |B| + [(t2 − s)α+β−1 − (t1 − s)α+β−1 ]g(s, x(s))ds Γ(α + β) 0 Z t2 |B| + (t2 − s)α+β−1 g(s, x(s))ds Γ(α + β) t1 h Z 1 (1 − s)α−δ−1 + |Q|[(t2 )α−1 − (t1 )α−1 ] |A| |f (s, x(s))|ds Γ(α − δ) 0 Z 1 (1 − s)α−δ+β−1 |g(s, x(s))|ds + |B| Γ(α − δ + β) 0 Z η Z η i (η − s)α−δ (η − s)α−δ+β + |A| |f (s, x(s))|ds + |B| |g(s, x(s))|ds Γ(α − δ + 1) Γ(α − δ + β + 1) 0 0 |A| Z t1 [(t2 − s)α−1 − (t1 − s)α−1 ]p1 (s)ψ1 (r)ds ≤ Γ(α) 0 8 B. AHMAD, S. K. NTOUYAS + |A| Γ(α) Z t2 (t2 − s)α−1 p1 (s)ψ1 (r)ds t1 |B| + Γ(α + β) Z |B| Γ(α + β) Z + t1 [(t2 − s)α+β−1 − (t1 − s)α+β−1 ]p2 (s)ψ2 (r)ds 0 t2 (t2 − s)α+β−1 p2 (s)ψ2 (r)ds t1 h Z + |Q|[(t2 )α−1 − (t1 )α−1 ] |A| 1 0 1 Z + |B| Z EJDE-2013/60 0 η + |A| 0 (1 − s)α−δ−1 p1 (s)ψ1 (r)ds Γ(α − δ) (1 − s)α−δ+β−1 p2 (s)ψ2 (r)ds Γ(α − δ + β) Z η i (η − s)α−δ+β (η − s)α−δ p1 (s)ψ1 (r)ds + |B| p2 (s)ψ2 (r)ds . Γ(α − δ + 1) Γ(α − δ + β + 1) 0 Obviously the right hand side of the above inequality tends to zero independently of x ∈ Br as t2 − t1 → 0. As U satisfies the above assumptions, therefore it follows by the Arzelá-Ascoli theorem that U : C([0, 1], R) → C([0, 1], R) is completely continuous. The result will follow from the Leray-Schauder nonlinear alternative (Lemma 1.4) once we have proved the boundendness of the set of all solutions to equations x = λUx for λ ∈ [0, 1]. Let x be a solution. Then, for t ∈ [0, 1], and using the computations in proving that U is bounded, we have |x(t)| o 1 |Q| |Q| + + Γ(α + 1) Γ(α − δ + 1) Γ(α − δ + 2) n o 1 |Q| |Q| + |B|ψ2 (kxk)kp2 kL1 + + . Γ(α + β + 1) Γ(α − δ + β + 1) Γ(α − δ + β + 2) = |λ(Ux)(t)| ≤ |A|ψ1 (kxk)kp1 kL1 n Consequently, kxk ≤ 1. |A|Λ1 ψ1 (kxk)kp1 kL1 + |B|Λ1 ψ2 (kxk)kp2 kL1 In view of (A4), there exists M such that kxk = 6 M . Let us set U = {x ∈ C([0, 1], X) : kxk < M }. Note that the operator U : U → C([0, 1], R) is continuous and completely continuous. From the choice of U , there is no x ∈ ∂U such that x = λU(x) for some λ ∈ (0, 1). Consequently, by the nonlinear alternative of Leray-Schauder type (Lemma 1.4), we deduce that U has a fixed point x ∈ U which is a solution of the problem (1.1). This completes the proof. Example. Consider a boundary-value problem of integro-differential equations of fractional order with nonlocal fractional boundary conditions given by −D5/2 x(t) = Af (t, x(t)) + BI β g(t, x(t)), D1/4 x(0) = 0, D5/4 x(0) = 0, D1/4 x(1) = t ∈ [0, 1], Z 0 η D1/4 x(s)ds, (1.7) EJDE-2013/60 NONLOCAL FRACTIONAL BOUNDARY-VALUE PROBLEMS where n = 3, A = B = 1, β = 3/4, η = 2/3, f (t, x) = 1 −1 x + sin2 t. With the given data, we find that 2 tan Q= 3|x|(2+|x|) 8(1+|x|) 9 + 4t, g(t, x) = Γ(α − δ + 1) = 1.037485, (α − δ − η α−δ )Γ(α) and 1 η α−δ+1 i tα + |Q|tα−1 + Γ(α + 1) Γ(α − δ + 1) Γ(α − δ + 2) t∈[0,1] h io α+β t 1 η α−δ+β+1 + |B| + |Q|tα−1 + Γ(α + β + 1) Γ(α − δ + β + 1) Γ(α − δ + β + 2) = 1.043555, Ω = sup n h |A| and L1 = 3/4, L2 = 1/2 as |f (t, x) − f (t, y)| ≤ 34 |x − y|, |g(t, x) − g(t, y)| ≤ 12 |x − y|. Clearly L = max{L1 , L2 } = 3/4 and L < 1/Ω. Thus all the assumptions of Theorem 1.2 are satisfied. Hence, by the conclusion of Theorem 1.2, the problem (1.7) has a unique solution. 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Qian; Positive Solutions for Fractional Differential Equations from Real Estate Asset Securitization via New Fixed Point Theorem, Abstr. Appl. Anal. 2012 (2012), Article ID 842358, 11 pages. Bashir Ahmad Department of Mathematics, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia E-mail address: bashirahmad qau@yahoo.com Sotiris K. Ntouyas Department of Mathematics, University of Ioannina, 451 10 Ioannina, Greece E-mail address: sntouyas@uoi.gr