On the Nonlinear Neutral Conformable Fractional Integral-Differential Equation ()
1. Introduction
The theory of fractional calculus has played a major role in control theory, fluid dynamics, biological systems, economics and other fields [1] [2] [3]. It serves as a valuable tool for the description of memory and hereditary properties of various materials and processes. In recent years, plenty of interesting results have been observed for the Riemann-Liouville and Caputo type fractional derivatives.
The definition of the conformable fractional derivative and integral was introduced in 2014 by Khalil et al. [4]. Compared with Riemann-Liouville and Caputo type fractional derivatives, the conformable fractional derivative satisfies the Leibniz rule and chain rule, and can be converted to classical derivative [5]. This is of great help to study fractional differential equations. In the past few years, the conformable fractional derivative has been used in the field of fractional newtonian mechanics, heat equation, biology and so on, and the results are abundant. The conformable fractional optimal control problems with time-delay were studied, which proved that the embedding method, embedding the admissible set into a subset of measures, can be successfully applied to nonlinear problems [6]. Alharbi et al. utilized the homotopy perturbation method to solve a model of Ambartsumian equation with the conformable derivative and gave the approximate solution of equation [7]. The conformable fractional derivative was utilized to solve the time-fractional Burgers type equations approximately [8].
Over these years, there has been a significant development in fractional functional differential equations. Among them, Li, Liu and Jiang gave sufficient conditions of the existence of positive solutions for a class of nonlinear fractional differential equations with caputo derivative [9]. Guo et al. studied fractional functional differential equation with impulsive, then they obtained existence, uniqueness, and data-dependent results of solutions to the equation [10]. The existence of positive periodic solutions was given by Zhang and Jiang, for n-dimensional impulsive periodic functional differential equations [11]. In addition, the fractional stochastic functional system driven by Rosenblatt process was investigated by Shen et al., and they obtained controllability and stability results [12].
Time-delay is part of the theoretical fields investigated by many authors, including unbounded time-delay, bounded time-delay, state-dependent time-delay and others. In 2009, the existence and uniqueness of solutions of the Caputo fractional neutral differential equations with unbounded delays were discussed [13]. In 2011, Li and Zhang considered the Caputo fractional neutral integral-differential equations with unbounded delay, which used the fixed point theorem to study the existence of mild solutions of equations [14]. The caputo fractional neutral integral-differential equations with unbounded delay were discussed in 2013 [15]. The paper used Monch’s fixed point theorem via measures of non-compactness to study the existence of solutions of equations.
Based on the above research background and relevant discussions, we found that few people used conformable derivative to study fractional differential equations with time-delay. In 2019, Mohamed I. Abbas gave the existence of solutions and uniqueness of solution for fractional neutral integro-differential equations by the Hadamard fractional derivative of order
and the Riemann-Liouville integral [16]. In this paper, we will discuss the nonlinear neutral fractional integral-differential equation in the frame of the conformable derivative of order
and the comformable integral. Then we make the condition 3 weaker to improve feasibility. Considering the following equation:
(1.1)
where
denotes the conformable fractional derivative of order
,
,
denotes the conformable fractional integral with order
,
,
,
.
are constants. And for any
, we denote by
the element of
and is defined by
,
. Here
represents the history of the state from time
up to the present time t.
are continuous functions that satisfy some hypotheses given later,
.
The rest of this paper is organized as follows: In Section 2, we introduce the concepts and basic properties of conformable fractional integral and derivative. In Section 3, we give existence results for the solution and sufficient conditions for uniqueness solution by Leray-Schauder nonlinear alternative and Banach contraction mapping principle. In Section 4, the numerical simulation is showed to illustrate the results.
Notations:
denotes all continuous functions that mapped from
to R and R denotes all real numbers.
denotes all positive real numbers.
2. Preliminaries
In this section, we present some necessary definitions and lemmas to establish our main results.
Definition 2.1. ( [5] ) For a function
, the conformable fractional integral of order
of the function w is defined as follows:
If
,
can be written as
.
Definition 2.2. ( [5] ) For a function
, the conformable fractional derivative of order
of the function w is defined as follows:
where
denotes the smallest integer greater than or equal to
. If
,
can be written as
.
Lemma 2.3 ( [4] ) If function l is
times differential at a point
for
,
, then
1)
, for all constant functions
;
2) l is
times differential simultaneously, then
.
Lemma 2.4. ( [5] )
1) For a function
, if
is continuous, then for any
, we have
2) For a function
, if w is
times differentiable, then for any
, we have
Lemma 2.5. ( [4] ) If
, functions
,
are
times differentiable at a point
, then
1)
2)
3)
4)
Lemma 2.6. ( [17] ) (The nonlinear alternative of Leray-Schauder type) Let C be a Banach space,
be a closed, convex subset of C, and P be an open subset of
,
. If
is a continuous, compact map. Then
1) A has a fixed point in P, or
2) There is a
(the boundary of P in
) and
, such that
.
Lemma 2.7. Let
be a continuous function, then the fractional differential equation
(2.1)
is equivalent to the integral-differential equation
(2.2)
where
,
.
Proof. Consider Equation (2.1), for any
,
Transforming
times conformable fractional integral on both sides of the equation and using Lemma 2.4, since
, we have
where
,
. The proof is completed. □
3. Main Results
In this section, we give several results about the fractional integral-differential Equation (1.1).
If
is Banach Space, the norm is defined as
.
Let
. Giving the definition of the operator
,
(3.1)
where
,
,
,
,
.
It should be noticed that Equation (1.1) has solutions if and only if the operator A has fixed points. So as to achieve the desired goals, we impose the following assumptions for the Equation (1.1).
(H1) There exist functions
and continuous non decreasing functions
, such that, for any
,
(H2) Functions
are continuous. There exist positive functions
with bounds
,
,
, respectively such that
(H3) There exists constant
,
, such that
(H4)
We give an existence result based on the nonlinear alternative of Leray-Schauder type applied to a completely continuous operator.
Theorem 3.1. Suppose that the assumptions (H1)-(H3) are satisfied, then the Equation (1.1) has at least one solution.
Proof. The operator A is defined as (3.1). Define
Firstly, we prove that operator A is uniformly bounded. For any
,
,
, and
, by (H1), we have
For any
and
, we have
Denote
, then
This implies that the operator A is uniformly bounded in D.
Besides, we need to prove that AD is an equicontinuous set. Let
be a sequence such that
in D. Then, for any
, we have
By (H2), functions
are uniformly continuous, thus, we have
For any
, it is obvious that
Therefore,
is continuous and uniformly continuous for
, which implies that
is equicontinuous for
, A is continuous in
.
Furthermore, we consider
, for any
,
.
Case 1. If
, for any
and
,
, we have
If
, then
.
Case 2. If
, for any
and
,
,
holds for any
, we have
Since
is a continuous function, if
, then we have
. If
, then
.
Case 3. If
, for any
and
,
Since
is continuous function, if
, then
.
From what has been discussed above, AD is equicontinuous. By Arzelá-Ascoli theorem, AN is compact, then A is completely continuous on X.
For any
and
,
, we have
For any
, by assumption (H1), we have
Consider the assumption (H3), there exists
. Define set
. We can show that
is continuous and completely continuous. Assuming there exists
and
, such that
. Then we have
.
By Lemma 2.6, A has a fixed point in P, which implies that there exists at least one solution to the Equation (1.1). The proof is completed. □
We will give the uniqueness result of solutions of Equation (1.1):
Theorem 3.2. Suppose that the assumptions (H2) and (H4) are satisfied, then the Equation (1.1) has a unique solution.
Proof. The operator A is defined as (3.1). For any
and
, by (H2), we have
For any
,
By (H4), A is a contraction mapping, then Equation (1.1) has a unique solution. The proof is completed. □
4. An Illustrative Example
This section presents an example where we apply Theorems 3.1 and 3.2 to some particular cases.
Example 4.1. Consider the fractional integral-differential equation
(4.1)
where
denotes the conformable fractional derivative of order
,
denotes the conformable fractional integral of the order
,
. If
, then for any
, we define
,
. Functions
The continuous function
satisfies the condition that
.
For any
,
, we have
For any
, we have
For any
,
, if
, we have
Consequently, by Theorem 3.1, the Equation (4.1) has at least one solution.
For continuous functions column
,
,
, we have
For continuous functions
,
, we have
For any
, we have
Thus, by Theorem 3.2, the Equation (4.1) has a unique solution.
5. Conclusion
The conformable fractional derivative brings great convenience to the study of fractional functional differential equations due to its unique properties. This paper uses conformable derivative to study the fractional neutral integro-differential equations, and obtains the results of the existence of the solution and the sufficient conditions for the uniqueness of the solution.