Electronic Journal of Differential Equations, Vol. 2015 (2015), No. 166, pp. 1–8. ISSN: 1072-6691. URL: http://ejde.math.txstate.edu or http://ejde.math.unt.edu ftp ejde.math.txstate.edu EXISTENCE OF LOCAL AND GLOBAL SOLUTIONS FOR HADAMARD FRACTIONAL DIFFERENTIAL EQUATIONS MENGMENG LI, JINRONG WANG Abstract. In this article, we study a class of Hadamard fractional differential equations and give sufficient conditions on the existence of local and global of solutions. 1. Introduction Let 0 ≤ γ < 1, 1 < a < T and G be an open set in R. Denote a Banach space by Cγ,ln [a, T ] := {µ(x) : (ln xa )γ µ(x) ∈ C[a, T ]} endowed with the norm kµkCγ,ln = k(ln xa )γ µ(x)kC . In this article, we study the existence of local and global solutions to the Hadamard type fractional differential equation α H Da,x y(x) = f (x, y(x)), α−1 + H Da,x y(a ) = c, 0 < α < 1, x ∈ J, c ∈ R, (1.1) α where J = [a, a + h], h > 0 or [a + ∞) and the symbol H Da,x y(x) is defined by Z x 1 d x dτ α x (ln )−α y(τ ) . H Da,x y(x) = Γ(1 − α) dx a τ τ We use the notation α−1 y(x) and = limx→a+ Ja,x Z x 1 x dt α−1 Ja,x y(x) = (ln )α−1 y(t)) . Γ(α) 1 t t α−1 + H Da,x y(a ) Following [1, Theorem 3.28], the solution y ∈ C1−γ,ln [a, a + h] of (1.1) satisfies Z x 1 x dτ y(x) = y0 (x) + (ln )α−1 f (τ, y(τ )) , x ∈ (a, a + h] (1.2) Γ(α) a τ τ c where y0 (x) = Γ(α) (ln xa )α−1 , if f : (a, a + h] × G → R and f (x, y) ∈ Cγ,ln [a, a + h] for any y ∈ G. Inspired by the work in [1, 2, 3], we examine other explicit sufficient conditions on the nonlinear term f to guarantee the local existence of solutions in Cγ,ln [a, a+h] and global existence of solutions in Cγ,ln [a, +∞). 2010 Mathematics Subject Classification. 26A33, 34A12. Key words and phrases. Hadamard fractional differential equation; local solution; global solution. c 2015 Texas State University - San Marcos. Submitted February 2, 2015. Published June 17, 2015. 1 2 M. LI, J. WANG EJDE-2015/166 2. Main results The following equality will be used in the sequel. Lemma 2.1 ([4, p.296]). Let α, β, γ, p > 0, then Z x xθ p(γ − 1) + 1 (xα − sα )p(β−1) sp(γ−1) ds = B , p(β − 1) + 1 , α α 0 R1 where θ = p[α(β − 1) + γ − 1] + 1 and B[ξ, η] = 0 sξ−1 (1 − s)η−1 ds. x > 0, Let B = {y ∈ R : ky − y0 (x)kCγ,ln ≤ b} where b will be chosen latter. Define D = {(x, y) ∈ R × R : x ∈ J, y ∈ B}. We assume that f : D → R satisfies the following conditions: (H1) f (x, y) is Lebesgue measurable with regard to x on J and f (x, y) is continuous with respect to y on B. (H2) there exists m(·) ∈ Lq (J), q > 1 such that |f (x, y)| ≤ m(x), for arbitrary x ∈ J, y ∈ B. Now we use Picard iterative approach to derive the existence of a local solutions to (1.1). Theorem 2.2. Assume that (H1)–(H2) hold for J = [a, a + h] and p, q, α satisfy p(α − 1) + 1 > 0, p1 + 1q = 1. Then (1.1) has a solution in Cγ,ln [a, a + h] for some h > 0. Proof. To achieve our aim, we divide our proof into three steps. Step 1. Linking our assumptions and using Hölder inequality via p(α − 1) + 1 > 0 and p1 + 1q = 1, one can obtain s Z x dt a1−p hp(α−1)+1 1/p |(ln x − ln τ )α−1 f (τ, y(τ ))| ≤ km(·)kLq [a,a+h] , (2.1) τ p(α − 1) + 1 a where we use basic inequalities: ln u − ln v ≤ u − v for u ≥ v > 1 and [5, Lemma 2.2], Z x a1−p (ln x − ln a)p(α−1)+1 . (2.2) (ln x − ln τ )p(α−1) τ −p dτ ≤ p(α − 1) + 1 a This proves that (ln x − ln τ )f (τ, y(τ )) is Lebesgue integrable with respect to τ ∈ [a, x] for arbitrary x on J, provided that y(τ ) is Lebesgue measurable on the interval [a, a + h]. Step 2. For a given M > 0, there exists a h0 > 0 satisfying Z a+h0 mq (τ )dτ ≤ M q , (2.3) a 0 1 p(α−1)+1 }. , T, [ MbΓ(α)(p(α−1)+1) ap−1 (ln T −ln a)γ ] whenever h = min{h For δ to be chosen latter, define 0, if a ≤ x < a + δ, 0 < δ < nh , c (ln x )α−1 , if a + δ ≤ x < a + h , a n yn (x) = Γ(α) R x− nh c x α−1 1 x α−1 + Γ(α) a (ln τ ) f (τ, yn (τ )) dτ Γ(α) (ln a ) τ , h if a + n ≤ x ≤ a + h. EJDE-2015/166 EXISTENCE OF LOCAL AND GLOBAL SOLUTIONS We show that yn (x) is continuous on [a, a + Case 1. For a < a + δ ≤ x1 < a + h n 2h n ] 3 for all n. < x2 ≤ a + h, |c| x2 x1 (ln )α−1 − (ln )α−1 Γ(α) a a Z x2 − nh 1 x2 dτ + (ln )α−1 |f (τ, yn (τ ))| Γ(α) a τ τ := I1 + I2 . |yn (x2 ) − yn (x1 )| ≤ 2−α For each ε > 0, there exists 0 < δ1 < [ aεΓ(α)δ 2|c|(1−α) ] such that for all x2 − x1 ≤ δ1 and for all n, we derive that x2 x1 |c| x2 x1 x1 x2 |c| |χ( ) − χ( )| ≤ |χ0 (ξ)|| − |, ξ ∈ ( , ) Γ(α) a a Γ(α) a a a a |c|(1 − α)(x2 − x1 ) ≤ Γ(α)(a + δ)(ln(a + δ) − ln a)2−α |c|(1 − α)(x2 − x1 ) < < ε/2, Γ(α)a(ln(a + δ) − ln a)2−α I1 = where χ(x) = (ln x − ln a)α−1 and χ0 (x) = (α − 1)(ln x − ln a)α−2 xa . p p 1 ] p(α−1)+1 such that for all For any ε > 0, there exists 0 < δ2 < [ ε Γ 2(α)(p(α−1)+1) p a1−p M p h x2 − n − a ≤ x2 − x1 ≤ δ2 and for all n, we use (2.2) and (2.3) to obtain 1 Γ(α) Z 1 ≤ Γ(α) Z I2 = h x2 − n (ln x2 α−1 dτ ) |f (τ, yn (τ ))| τ τ (ln x2 α−1 dτ ) m(τ ) τ τ a h x2 − n a M a1−p (ln(x2 − nh ) − ln a)p(α−1)+1 1/p ≤ Γ(α) p(α − 1) + 1 1−p M a (x2 − nh − a)p(α−1)+1 1/p ≤ < ε/2, Γ(α) p(α − 1) + 1 where we use that ln u − ln v ≤ u − v, u > v > 1 again in the last inequality. From above, we can choose δ̄ =min{δ1 , δ2 , h/n} such that for all x2 − x1 ≤ δ̄ and for all n, such that |yn (x2 ) − yn (x1 )| ≤ I1 + I2 < ε. Case 2. For a + h n ≤ x1 < x2 ≤ a + 2h n . One has |yn (x2 ) − yn (x1 )| Z x1 − nh 1 x2 x1 dτ ≤ S1 + (ln )α−1 − (ln )α−1 |f (τ, yn (τ ))| Γ(α) a τ τ τ Z x2 − nh 1 x2 dτ + (ln )α−1 |f (τ, yn (τ ))| Γ(α) x1 − nh τ τ := S1 + S2 + S3 . 4 M. LI, J. WANG EJDE-2015/166 h i h 2−α aεΓ(α)( n ) such that for all x2 − x1 ≤ δ¯1 , For each ε > 0, there exists 0 < δ¯1 < 3|c|(1−α) we have |c|(1 − α)(x2 − x1 ) S1 ≤ < ε/3. Γ(α)a(ln(a + nh ) − ln a)2−α 1 i h p p (p(α−1)+1) p(α−1)+1 For each ε > 0, there exists 0 < δ¯2 < ε Γ(α) such that for p p 1−p 3 M a ¯ all x2 − x1 ≤ δ2 , by using the similar estimation methods of I2 we have Z h x1 − n dτ x1 x2 α−1 ) − (ln )α−1 |f (τ, yn (τ ))| τ τ τ a Z x1 − nh 1 x2 dτ x1 ≤ (ln )α−1 − (ln )α−1 m(τ ) Γ(α) a τ τ τ Z x1 − nh Z x1 − nh 1/p i h 1/p M x2 x1 ≤ − (ln )p(α−1) τ −p dτ (ln )p(α−1) τ −p dτ Γ(α) τ τ a a h p(α−1)+1 i1/p M (ln x2 − ln x1 ) ≤ Γ(α) ap−1 (p(α − 1) + 1) M h (x2 − x1 )p(α−1)+1 i1/p ≤ < ε/3. Γ(α) ap−1 (p(α − 1) + 1) S2 = 1 Γ(α) (ln p p 1 (p(α−1)+1) p(α−1)+1 , such that for For each ε > 0, there exists 0 < δ¯3 < [ ε Γ(α) ] 3p M p a1−p all x2 − x1 ≤ δ¯3 , by using the similar estimation methods of I2 we have Z x2 − nh x2 1 dτ (ln )α−1 |f (τ, yn (τ ))| S3 = Γ(α) x1 − nh τ τ Z x2 − nh x2 dτ 1 (ln )α−1 m(τ ) ≤ Γ(α) x1 − nh τ τ ≤ M a1−p (x2 − x1 )p(α−1)+1 1/p < ε/3. Γ(α) p(α − 1) + 1 From the above, we choose δ̄¯ = min{δ¯1 , δ¯2 , δ¯3 , h/n} such that x2 − x1 ≤ δ̄¯, then |yn (x2 ) − yn (x1 )| ≤ S1 + S2 + S3 < ε. Therefore, we choose δ = min{δ̄, δ̄¯} will lead to yn (x) is continuous with regard to x on [a, a+ 2h n ] for all positive integers n. Note that (ln x − ln a)γ is continuous function, so yn (x)(ln x − ln a)γ is also continuous. c Nevertheless, for all x ∈ [a + δ, a + nh ], one has |yn (x) − Γ(α) (ln xa )α−1 | = 0, and for all x ∈ [a + nh , a + h], using Hölder inequality again, x c x (ln )γ |yn (x) − (ln )α−1 | a Γ(α) a Z x− nh 1 x x dτ ≤ (ln )γ (ln )α−1 |f (τ, yn (τ ))| Γ(α) a a τ τ ≤ (2.4) (ln(a + h) − ln a)γ a1−p M hp(α−1)+1 ≤ b, Γ(α)(p(α − 1) + 1) which implies that (x, yn (x)) ∈ D for all n. Therefore, {yn (x)}∞ n=1 defined on [a, a + h] is equicontinuous and uniformly bounded. EJDE-2015/166 EXISTENCE OF LOCAL AND GLOBAL SOLUTIONS 5 Step 3. By using Arzelò-Ascoli lemma and Step 2, there must exist {ynk (x)}∞ k=1 := ∞ ∞ {yk (x)}∞ contained in {y (x)} , such that {y (x)} is uniformly convergent n k n=1 k=1 k=1 to y(x) which is continuous with regard to x on [a, a + h]. Now we only need to prove that this limit function y(x) is a solution of (1.2). For each ε > 0, there exists K1 > 0, such that for all k > K1 , and x ∈ [a, a + h], we have Γ(α + 1)ε . (2.5) |f (x, yk (x)) − f (x, y(x))| < 2(ln(a + h) − ln a)γ hα Note that (ln x − ln a)γ |yk (x) − y(x)| Z x 1 x x dτ (ln )γ (ln )α−1 |f (τ, yk (τ )) − f (τ, y(τ ))| ≤ Γ(α) a a τ τ Z x 1 x γ x α−1 dτ + (ln ) (ln ) |f (τ, yk (τ ))| Γ(α) x− hk a τ τ := S4 + S5 . Using (2.5) one obtains, Z x x dτ 1 x S4 = (ln )γ (ln )α−1 |f (τ, yk (τ )) − f (τ, y(τ ))| Γ(α) a a τ τ γ Z a (ln(a + h) − ln a) x ≤ (ln )α−1 |f (τ, yk (τ )) − f (τ, y(τ ))|d(ln x − ln τ ) Γ(α) τ x γ α (ln(a + h) − ln a) h Γ(α + 1)ε ≤ < ε/2. aΓ(α) 2(ln(a + h) − ln a)γ hα Also there exists −1 ap−1 εp Γ(α)p (p(α − 1) + 1) p(α−1)+1 , 0 < K2 = h p p pγ 2 M (ln(a + h) − ln a) such that for all k > K2 , Z x 1 x dτ x S5 = (ln )γ (ln )α−1 |f (τ, yk (τ ))| Γ(α) x− hk a τ τ Z x 1/p γ (ln(a + h) − ln a) M x ≤ (ln )p(α−1) τ −p dt Γ(α) τ x− h k h p(α−1)+1 1/p γ (k) (ln(a + h) − ln a) M ≤ < ε/2. Γ(α) ap−1 (p(α − 1) + 1) Hence, taking K = max{K1 , K2 } and for all k > K, one arrives at kyk (x) − y(x)kCγ,ln < ε. Consequently, y(x) satisfies (1.2) which means that there at least exists a solution of (1.1). Next, we give an existence and uniqueness theorem, using the assumption (H3) there exists a µ(·) ∈ Lq (J), 1q = 1 − p1 , p > 1 such that |f (x, y) − f (x, z)| ≤ µ(x)|y − z| for x ∈ J and y, z ∈ B, 1 Theorem 2.3. Let 0 ≤ γ ≤ min{α − 1 + p1 , 2p }, p > 1. Assume that (H1)–(H3) are satisfied for J = [a, a + h]. Then (1.1) has a unique solution in Cγ,ln [a, a + h] for some h > 0. 6 M. LI, J. WANG EJDE-2015/166 Proof. There exits h∗ > 0, such that for all x ∈ [a, a + h∗ ], Z a+h∗ Z x µq (τ )dτ ≤ µq (τ )dτ < g q . a (2.6) a Let Ψh = {y ∈ Cγ,ln [a, a + h] : ky(x) − y0 (x)kCγ,ln ≤ b, x ∈ [a, a + h]}, where h is the smaller one between h∗ and h obtained in Theorem 2.2. Note Ψh endowed with k · kCr ln is a Banach space. Define Z x 1 x dτ ψ(y) = y0 (x) + (ln )α−1 f (τ, y(τ )) , ∀x ∈ [a, a + h]. Γ(α) a τ τ Firstly, assume that a ≤ x1 < x2 ≤ a+h, then according to the proof in Step 2 of Theorem 2.2, we obtain that ψ(y) is continuous with regard to x on [a, a + h]. Note that (ln x − ln a)γ is continuous function, so ψ(y)(ln x − ln a)γ is also continuous. Secondly, it following (2.4) that ψ(y) ∈ Ψh with y ∈ Ψh . Thirdly, the condition 1 1 }, p > 1 implies that p(α − 1 − γ) + 1 > 0, 0 ≤ γ < 2p . 0 ≤ γ ≤ min{α − 1 + p1 , 2p For any y1 , y2 ∈ Ψh , then using Hölder inequality, (2.6) and Lemma 2.1, we have (ln x − ln a)γ |ψ(y2 ) − ψ(y1 )| Z (ln x − ln a)γ x dτ x ≤ (ln )α−1 µ(τ )|y1 (τ ) − y2 (τ )| Γ(α) τ τ a Z (ln(a + h) − ln a)γ x τ −γ dτ x α−1 ≤ (ln ) µ(τ ) ky1 − y2 kCr ln (ln ) Γ(α) τ a τ a Z 1/p x (ln(a + h) − ln a)γ ga1−p ln x−ln a ky1 − y2 kCγ ln (ln − t)p(α−1) t−pγ dt ≤ Γ(α) a 0 1/p (ln(a + h) − ln a)γ ga1−p x ≤ (ln )p(α−1−γ)+1 B[1 − pγ, p(α − 1) + 1] Γ(α) a × ky1 − y2 kCγ ln hγ g p(α−1−γ)+1 1 (h B[ , p(α − 1) + 1])1/p ky1 − y2 kCγ ln Γ(α) 2 1 1/p i h hα−1+ p g 1 ky1 − y2 kCγ ln , = a1−p B[ , p(α − 1) + 1] Γ(α) 2 ≤ a1−p where we use that 1 1 1 ⇒ 1 − pγ > ⇒ t1−pr ≤ t 2 (0 ≤ t ≤ 1), 2p 2 Z 1 B[1 − pγ, p(α − 1) + 1] = t−pγ (1 − t)p(α−1) dt γ< 0 Z ≤ 0 Obviously, one can choose h≤ 1 1 1 t− 2 (1 − t)p(α−1) dt = B[ , p(α − 1) + 1]. 2 p p(α−1)+1 Γ(α) , g(B[ 21 , p(α − 1) + 1])1/p then 1 1/p hα−1+ p g 1 ≤ 1. B[ , p(α − 1) + 1] Γ(α) 2 EJDE-2015/166 EXISTENCE OF LOCAL AND GLOBAL SOLUTIONS 7 Therefore, kψ(y2 ) − ψ(y1 )kCγ ln ≤ a1−p ky1 − y2 kCγ ln . Obviously, a1−p < 1 due to a, p > 1, applying the Banach Contractive Mapping Principle, one concludes that there exists a unique y ∗ (x) ∈ Ψh , such that (1.2). The proof is compete. Next, we give the existence of a global solution, using the assumption (H2’) there exist ω, ν > 0 such that |f (x, y)| ≤ ω + ν|y| for x ∈ (a, +∞) and y ∈ R. Theorem 2.4. Assume that (H1), (H2’), (H3) hold for J = (a, +∞). Further, 1 }, p > 1. Then (1.1) has a unique solution choose γ = 1 − α ≤ min{α − 1 + p1 , 2p in Cγ,ln [a, +∞). Proof. It follows (H2’) that f is locally bounded in the domain D. By Theorem 2.3, (1.1) has a unique solution in Cγ,ln [a, a+h]. Next, we present proof by contradiction. Assume that the solution y(x) admits a maximal existence interval, denoted by (a, T ) ⊂ (a, +∞). To achieve our aim, it is sufficient to verify that kykCγ,ln is bounded. In fact, (ln x − ln a)γ |y(x)| Z x |c| 1 x x dτ ≤ + (ln )γ (ln )α−1 |f (τ, y(τ ))| Γ(α) Γ(α) a a τ τ Z x 1 x dτ |c| x + ≤ (ln )γ (ln )α−1 (ω + ν|y(τ )|) Γ(α) Γ(α) a a τ τ 1−α α |c| ω(ln T − ln a) (T − a) ≤ + Γ(α) Γ(a + 1) Z x x dτ ν (ln )α−1 (ln x − ln a)γ |y(τ )| + Γ(α) a τ τ Z x ω(T − a) ν dτ |c| x + + ≤ (ln )α−1 (ln x − ln a)γ |y(τ )| . Γ(α) Γ(α + 1) Γ(α) a τ τ By applying the generalized Gronwall inequality from [3, Corollary 3.4], one can conclude that there exists l := Eα (ν(ln T )α ) > 0 (Eα denotes Mittag-Leffler function) such that (ln x − ln a)γ |y(x)| ≤ l( |c| ω(T − a) + ) := ρ < +∞. Γ(α) Γ(α + 1) This implies that kykCγ,ln < b on [a, T ) when b is chosen as a larger number than b=ρ+ |c| . Γ(α) (2.7) This contradicts the assumption that (a, T ) is the maximal existence interval. The proof is complete. To finish this article, we give an example that illustrates our theoretical results. Consider 4|y| 3/4 2 sin x, x ∈ J = (e, e2 ] or (e, +∞), H De,x y(x) = x + 1 + |y| (2.8) −1/4 + H De,x y(e ) = 1, 8 M. LI, J. WANG EJDE-2015/166 where α = 3/4, T = e2 , γ = 1/4, a = e, c = 1, and p = q = 2. 4|y| Define f (x, y) = x2 + 1+|y| sin x, µ(x) = 4 and ω = e2 + 4 and ν = 0. Thus |f (x, y) − f (x, z)| ≤ µ(x)|y − z| and |f (x, y)| ≤ ω. Then l := Eα (0) = 1 (see [6, 2 2 −e) 2 Lemma 2]) and b = Γ(3/4) + (e +4)(e (see (2.7)). Γ(7/4) R 2e Let h0 = h∗ = e. Set M 2 = e (e4 + 4)2 dx = e(e4 + 4)2 (see (2.3)) and g 2 = R 2e 1 16dx = 16e (see (2.6)). Moreover, one can find γ = 1 − α = min{α − 1 + p1 , 2p }. e • According to Theorem 2.3, (2.8) admits a unique solution y ∈ C 14 ,ln (e, e + h] where 1 n h bΓ(α)(p(α − 1) + 1) i p(α−1)+1 h = min h0 , T, , M ap−1 p o Γ(α) p(α−1)+1 1 1/p g(B[ 2 , p(α − 1) + 1]) 2 2 n h ( 2 + (e +4)(e −e) )Γ(3/4) i2 h i4 o Γ(3/4) Γ(3/4) Γ(7/4) √ 4 = e, e2 , . , √ q 2 e(e + e)e 4 e B[ 1 , 1 ] 2 2 • According to Theorem 2.4, (2.8) has a unique solution y ∈ C 14 ,ln (e, +∞). Acknowledgments. This work is supported by the National Natural Science Foundation of China (11201091) and by the Outstanding Scientific and Technological Innovation Talent Award of Education Department of Guizhou Province ([2014]240). References [1] A. A. Kilbas, H. M. Srivastava, J. J. Trujillo; Theory and applications of fractional differential equations, Mathematics Studies, vol. 204, North-Holland, Elsevier Science B. V., Amsterdam, 2006. [2] W. Lin; Global existence theory and chaos control of fractional differential equations, J. 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Mengmeng Li Department of Mathematics, Guizhou University, Guiyang, Guizhou 550025, China E-mail address: Lmm0424@126.com Jinrong Wang (corresponding author) Department of Mathematics, Guizhou University, Guiyang, Guizhou 550025, China E-mail address: sci.jrwang@gzu.edu.cn