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P. 125

Investigate the solution of an initial Hilfer fractional value problem
                    where                                     Let v, w ∈ C 1−κ (J , R), by hypothesis (Q1), we
                                                              have
                            |g (s, v)| ≤ ξ (s) .
                                                                    1−κ
                                                               (s − p)  (∆v (s) − ∆w (s))|
            Theorem 2. Suppose that the assumptions (Q1)
            and (Q2) are fulfilled. If (q − p) 1−κ  < 1, then the        = (s − p) 1−κ  |f (s, v (s)) − f (s, w (s))|
            IVP (1)–(2) possesses a solution in C 1−κ (J , R).           ≤ (s − p) 1−κ ψ D (|v (s) − w (s)|)

                            n                             o                       1−κ
            Proof. Let K = φ ∈ C 1−κ (J , R) : ∥φ∥     ≤ η ,             ≤ (s − p)   ψ D
                                                  C 1−κ

            where                                                          · (s − p) κ−1 ∥v − w∥     .
                                      σ
                       |φ 0 |     (q−p) β(κ,σ)                                                 C 1−κ
                       Γ(κ)  + Λ +   Γ(σ)    ∥ξ∥ C 1−κ
                   η ≥                              ,         Applying a maximum over s gives
                               1 − (q − p) 1−κ
                                                                   ∥∆v − ∆w∥       ≤ ψ D ∥v − w∥       .
            (q − p) 1−κ  < 1 and Λ = max(s − p)  1−κ f (s, 0).                C 1−κ              C 1−κ
                                      t∈J
            Certainly, K ⊂ C 1−κ (J , R) which is closed, con-  Hence, the operator ∆ is a non-linear contraction.
            vex, and bounded in nature.                       Step II: Operator Ω is a continuous and compact
                Now, in order to establish the existence result  on K into C 1−κ (J , R).
            for the IVP (1)–(2), let us consider the general-
                                                              First, to show Ω is continuous on K, consider a
            ized IVP involving HFD operator of order σ and
                                                              sequence {z n } in K converging to z ∈ K. Then,
            type τ, for z ∈ K, as follows:
                                                              it implies from the Lebesgue-dominated conver-
              σ,τ
             D + [φ (s) − f (s, φ (s))] = g (s, z (s)) ,  s ∈ J ,  gence theorem that
              p
                                                       (12)       lim Ωz n (s)
                  1−κ
                                          +
                 I + [φ (s) − f (s, φ (s))] (p ) = φ 0 ,  (13)   n→∞
                  p
                                                                               s
            where 0 < σ < 1, 0 ≤ τ ≤ 1 and κ = σ + τ − στ,                1   Z         σ−1
                                               +                 = lim           (s − w)   g (w, z n (w)) dw
            J = [p, q], for some fixed p, q ∈ R  and f, g ∈         n→∞ Γ (σ)
            C (J × R, R).                                                     p
            Assume that the hypotheses (Q1) and (Q2) hold                Z s
                                                                      1
            for the functions f and g. Using Lemma 9, we         =          (s − w) σ−1  lim g (w, z n (w)) dw
            get the equivalent non-linear VIE to the IVP            Γ (σ)             n→∞
                                                                         p
            (12)–(13) as                                                  s
                                                                      1  Z
                        φ 0       κ−1                                              σ−1
               φ (s) =      (s − p)   + f (s, φ (s))             =          (s − w)   g (w, z (w)) dw
                       Γ (κ)                                        Γ (σ)
                                                                         p
                               s
                          1   Z        σ−1                       = Ωz (s) ,   ∀s ∈ J .
                      +         (s − w)    g (s, z (w)) dw.
                         Γ (σ)
                              p                               This proves the continuity for Ω. Next, we prove
                                                       (14)   that ΩK is a uniformly bounded and equicontin-
                                                              uous set in K which implies the compactness of
            Consider the operators ∆ : C 1−κ (J , R) →
                                                              Ω on K.
            C 1−κ (J , R) and Ω : K → C 1−κ (J , R) defined
            as follows:                                       It   follows   from   the    hypothesis   (Q2)
                        φ 0        κ−1                        that
            (∆φ)(s) =       (s − p)   + f (s, φ (s)) , s ∈ J ,
                       Γ (κ)
                                                       (15)            1−κ
                                                                  (s − p)  Ωz (s)
            and
                               s
                          1   Z         σ−1
              (Ωz)(s) =          (s − w)   g (w, z (w)) dw,           (s − p) 1−κ  Z s
                         Γ (σ)                                                           σ−1
                              p                                  =               (s − w)   g (w, z (w)) ds
                                                                      Γ (σ)
                                                       (16)                   p
                     s ∈ J .                                        (s − p) 1−κ  Z s
                                                                 ≤               (s − w) σ−1  |g (w, z (w))| ds
            Hence, the equation (14) can be transformed as            Γ (σ)
                                                                              p
                 φ (s) = ∆φ (s) + Ωz (s) ,  s ∈ J .    (17)
                                                                                s
                                                                          1−κ
                                                                              Z
            Next, we will show that the operators ∆ and Ω        ≤  (s − p)      (s − w) σ−1 ξ (w) ds
            satisfy all the conditions of Theorem 1. The proof        Γ (σ)
                                                                              p
            is divided into the following steps.
             Step I: Operator ∆ is non-linear D−contraction.
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