Variational Method to p-Laplacian Fractional Dirichlet Problem with Instantaneous and Noninstantaneous Impulses

In this paper, a research has been done about the existence of solutions to the Dirichlet boundary value problem for p-Laplacian fractional differential equations which include instantaneous and noninstantaneous impulses. Based on the critical point principle and variational method, we provide the equivalence between the classical and weak solutions of the problem, and the existence results of classical solution for our equations are established. Finally, an example is given to illustrate the major result.


Introduction
Fractional calculus involves arbitrary order derivatives and integration, so it plays a very important role in various fields such as physical engineering, medical image processing, mathematics, chemical engineering, and electricity. For this reason, many scholars did research on the theory of fractional differential equations continuously and have made enormous achievements; readers who are interested in these kinds of researches can refer to relevant literature (see [1][2][3][4][5][6] and the references therein). Of course, in the science field, an impulsive phenomenon has also been spread widely when dealing with practical problems, and it has become a very effective tool for describing changes in sudden discontinuous jumps. In addition, from the perspective of the duration of the change, impulses can be divided into instantaneous impulses and noninstantaneous impulses. The difference between them is that the duration of the instantaneous impulse continuous change is relatively short compared to the duration of the entire process, and the noninstantaneous impulse change is to keep moving from any fixed point and at a certain time interval. In [7], Agarwal et al. provide a more detailed introduction to these two impulsive differential equations. We also noticed that some experts combine the theory of fractional calculus, of noncompactness, with Sadovskii's fixed-point theorem and even more excellent methods have obtained more and better properties for fractional order equations with impulsive conditions, which greatly promotes its development (see, for example, [8][9][10][11][12][13][14][15], and the references therein).
For a long time, many scholars have conducted in-depth research on instantaneous impulsive differential equations. By using fixed-point theorems, critical point theorems, and variational methods, they obtained the existence of solutions (see [16][17][18]). But in many cases, instantaneous impulses cannot describe the development of certain dynamics. In 2013, Hernández and O'Regan first proposed the concept of noninstantaneous impulsive differential equations (see [19]). Since then, the existence of solutions to noninstantaneous impulsive problems has been gradually expanded by using some methods such as fixed-point theory and analytical semigroup theory, but the variational structure of general noninstantaneous impulsive differential equations has not received widespread attention. Among them, the existence of solutions for second-order differential equations with instantaneous and noninstantaneous impulses was investigated. Tian and Zhang obtained the existence results through the principle of variation (see [20]). In addition, it is worth noting that by using the critical point theory and variational method, Zhao et al. proved the existence and multiplicity of nontrivial solutions to the problem of nonlinear nontransient impulsive differential equations (see [21]). At the same time, some scholars have obtained the existence results of solutions for noninstantaneous impulsive differential equations by variational methods (see [22][23][24]).
In [25], Zhang and Liu generalized linear fractional differential equations to nonlinearities on the interval t ∈ ðs i , t i + 1 and removed the restriction t D α−1 T ð C 0 D α t uð0ÞÞ = constant. By using a variational method, they considered the following Dirichlet problems with instantaneous and noninstantaneous impulse differential equations: In [26], Zhou et al. discussed the existence of solutions for fractional differential equations of p-Laplacian with instantaneous and noninstantaneous impulses. The innovation was that when p = 2, problem (2) can be regarded as problem (1), and when α = 1, it can be simplified to a more general integer order case. Finally, they got the classical solution and prove that the weak solution was equivalent to the classical solution: Motivated by the above-mentioned work, the paper focuses on the existence of solutions for the following p-Laplacian fractional differential equations with instantaneous and noninstantaneous impulses, and if D x F i ðt, uðtÞ − uðt i + 1ÞÞ = f i ðt, uðtÞÞ, the following problem reduces to (2): where α ∈ ð1/p, 1, p ≥ 2, t D α T , and C 0 D α T denote the right Riemann-Liouville fractional derivatives and left Caputo fractional derivatives. 0 = s 0 < t 0 < s 1 < t 1 < ⋯ < t N = T, I i ∈ CðR, RÞ, and there exists i ∈ f1, 2, ⋯, Ng such that Iðuðt i ÞÞ ≠ 0:f i ∈ Cððs i , t i+1 × R, RÞ, ϕ p : R ⟶ R is the p-Laplacian function defined as ϕ p ðsÞ = jsj p−2 sðs ≠ 0Þ, ϕ p ð0Þ = 0:λ ∈ L ∞ ½0, T, essinf t∈ð0;TÞ λðtÞ > −ðΓðα + 1Þ/T α Þ p . The nonlinear functions D x F i ðt, xÞ are the derivatives of F i ðt, xÞ, for every Journal of Function Spaces To the best of our knowledge, the instantaneous impulses start abruptly at point t i and the noninstantaneous impulses continue during the intervals ðt i , s i , and The rest of the paper is organized as follows. In Section 2, some basic knowledge and lemmas used in the latter are presented. In Section 3, we first give the equivalent form of solution of problem (3), and secondly, we establish the equivalence of the classical solution and the weak solution by using the critical point principle for the variational structure of problem (3) and finally prove the existence of solution. An illustrative example is given to show the practical usefulness of the analytical results in Section 4.

Preliminaries
In this section, we introduce some important definitions, lemmas, and theorems that are important to use later. For the definitions of the left and right fractional integrals and derivatives, we can refer to References [7,23].

Lemma 9.
Let X be a reflexive Banach space and let φ : X ⟶ ð−∞, +∞ be weakly lower semicontinuous on X.
If φ has a bounded minimizing sequence, then φ has a minimum on X.

Main Results
In this section, we further discuss the variational structure of problem (3) and define the functional φ to prove that the critical point of φ is the weak solution of problem (3). In addition, we also give the equivalence between weak solution and the classical solution of this problem. Finally, the 3 Journal of Function Spaces existence of classical solution for problem (3) is given by Theorem 16. For each i = 0, 1, 2, ⋯, N, the nonlinear functions F i satisfy the following assumptions: (H1). F i ðt, xÞ is measurable in t for every x ∈ R and continuously differentiable in x for a.e. t ∈ ðs i , t i+1 , and there exist functions k 1 ∈ CðR + , R + Þ, k 2 ∈ L 1 ððs i , t i+1 Þ, R + Þ such that (H2). There exist constants δ ∈ ð0, 2Þ, a > 0, and the functions (H3). There exist constants 0 , the following form is an equivalent form of the problem (3): Proof.
For v ∈ E α,p 0 , by (10) have We have As for problem (3), we have

Journal of Function Spaces
Above all, problem (3) has the following equivalent form: where Under condition (H1), for a.e. t ∈ ðs i , t i+1 , we have From (21), for all γ ∈ ð0, 1Þ, According to the mean value theorem and condition (H1), for some γ ∈ ð0, 1Þ, By the Lebesgue dominated convergence theorem, it is easy to show that ϕ i has a directional derivative at each point u: Thus, 0 , then fu k g converges uniformly to u for all t ∈ ½0, T, we have Therefore This yields that the critical points of φ are weak solutions of problem (3).
From Proposition 6, sequence fu k g ∞ k=1 is convergent uniformly to u in Cð½0, T, RÞ; thus, we have Proof. From the definition of classical solutions, without loss of generality, if u is a classical solution of problem (3), then it is a weak solution of (3). Conversely, let u ∈ E α,p 0 be a weak solution of (3); thus, uð0Þ = uðTÞ = 0 and (15) holds. Now, we prove that u is a classical solution of the problem (3). We take a test function v ∈ C ∞ 0 ðs i t i+1 satisfying vðtÞ = 0, where t ∈ ½0, s i Þ ∪ ½t i+1 , TÞ, i = 0, 1, 2, ⋯, N. Substituting vðtÞ into (15) and by Proposition 7, we have that is to say, Since u ∈ E α,p Because of D x F i ðt, uðtÞ − uðt i+1 ÞÞ ∈ Cððs i , t i+1 × R, RÞ, by (31), we have Therefore, In view of (15) and (31), we have that is, Without loss of generality, we take the test function By using (36) and (37), we have Hence, Then, combining with (37), we have Therefore, u is a classical solution of the problem (3). The proof is completed.  Journal of Function Spaces Proof. From Proposition 5, there exist constants A 2 , A 3 such that where Since p > 2, we get lim kuk α →+∞ φðuÞ = +∞, then φ is coercive. From Lemma 10 and Lemma 14 that φ satisfied all the conditions of Lemma 9, so φ has a minimum on E α,p 0 which is a critical point of φ. Since I i ðuðt i ÞÞ ≠ 0 ði = 1, 2, ⋯, NÞ, then u ≠ constant (u is a critical point of φ).
Therefore, problem (3) has at least one classical solution. The proof is completed.

Conclusions
In this paper, we use the variational method to discuss the existence of solutions for Dirichlet boundary value problems with instantaneous and noninstantaneous fractional impulsive differential equations, and the existence results of classical solution for our equations are shown. In addition to extending the linear differential operator to a nonlinear differential operator, it is more important to use the p-Laplacian operator; as far as the author knows, there is not much work to study the solution of the generalized p-Laplacian impulsive fractional system using the variational method. Compared with (2), (3) contains the existence results of (2) when D x F i ðt, uðtÞ − uðt i+1 ÞÞ ≡ f i ðt, uðtÞÞ. Without loss of generality, if p = 2, α = 1 it evolves into an integer order differential equation which has a certain auxiliary role in solving nonlinear similar problems in the future. At the same time, we also noticed the existence of multiple solutions or the existence of nontrivial solutions to the problem, so we will pay special attention in the following work. Overall, our work summarizes and supplements some of the results in the literature.

Data Availability
No data were used to support this study.

Conflicts of Interest
The authors declare that they have no competing interest.