1. Introduction
FCs ware first employed in 1695 when L’Hopital summarized his discoveries in a letter to Leibniz. Fractional calculus (FCs) was studied by several twentieth century authors, including Liouville, Grunwald, Letnikov, and Riemann. This field of mathematics, known as fractional differential equations, was invented by mathematicians as a pure branch of mathematics with just a few applications in mathematics. Fractional calculus is a well-established subject with applications in many applied sciences, such as visco-elasticity, medical, and environment, which leads the fractional differential equations to become extremely prevalent. We recommend the monographs [
1,
2,
3,
4,
5,
6,
7,
8] and the recently mentioned papers [
9,
10,
11,
12,
13,
14,
15,
16,
17]. It is worth noting that most of the works in the field of fractional differentiation focus mostly on R-L and Caputo types. See [
18,
19,
20,
21,
22].
In 1772, Russian scientists presented a general idea of stability, such as Lyapunov (1758–1817), where the general theme of his doctoral dissertation was movement stability, and his work soon spread all over Russia and later in the West. With the process of research, scientists entered the time delay, and the first to describe these systems with a time delay was the scientist (Boltzman), who studied its effect but did not refer to the time delay in realistic models.
In the early 1900s, a disagreement arose over the necessity of introducing time delays into systems to predict their future development, but this point of view contradicted the Newtonian traditions, which claimed that knowledge of the current values of all relevant variables should suffice for the prediction. Ulam and Hyers, on the other hand, recognized unknown types of stability known as ulam-stability. Hyer’s type of stability study contributes expressively to our understanding of population dynamics and fluid movement, see [
23].
In mathematics, differential inclusions relate to one or more functions and their derivatives. In applications, functions generally represent physical quantities, derivatives represent their rates of change, and differential inclusion defines the relationship between the two. Because these relationships are so common, differential equations play a prominent role in many disciplines, including engineering, physics, economics, and biology. The study of differential inclusions mainly consists of studying their solutions (the set of functions that satisfy the equation), and the properties of their solutions. The simplest differential inclusions can be solved by explicit formulas. However, many properties of solutions to particular differential inclusions may be determined without being exactly calculated. If a closed expression is not available for the solutions, the solutions may be numerically approximated using computers. Dynamical systems theory focuses on the qualitative analysis of systems described by differential equations and differential inclusions, while many numerical methods have been developed to determine solutions with a certain degree of precision.
Many of the basic laws of physics and chemistry can be formulated as differential equations. In biology and economics, differential equations are used to model the behavior of complex systems. The mathematical theory of differential equations developed first with the sciences in which the equations originated and where the results were put into practice. However, various problems which sometimes arise in quite distinct scientific fields may result in identical differential equations. Whenever this happens, the mathematical theory behind the equations can be seen as a unifying principle behind the various phenomena. For example, consider the propagation of light and sound in the atmosphere, and the waves on the surface of a pond. They can all be described by the same second-order partial differential equation, which is the wave equation, that allows us to think of light and sound as forms of waves, much like the familiar waves in water. Heat conduction, developed by Joseph Fourier, is governed by a second-order partial differential equation, the heat equation. It turns out that many diffusion processes, though apparently different, are described by the same equation; the Black–Scholes equation in finance, for example, is related to the heat equation [
24,
25]. In [
26], the authors were the first who developed the idea of the tripled fixed points. Karakaya et al. [
27] introduce tripled fixed points for a class of condensing operators in Banach spaces. In [
25], the authors studied the existence results for the following BVP.
where
denotes the Caputo fractional derivatives (CFDs) of order
,
are continuous functions,
is a cyclic permutation, and
In this work, motivated by [
28], we consider the following system of sequential fractional differential inclusions:
where
is a CFDs of order
,
are given continuous functions,
is the family of all non-empty subset of
,
and
.
The Caputo SFDEs with multi-point and integral boundary conditions discussed in this work are the most widely used Caputo fractional derivatives. The novelty and originality of this work is summarized by using Covitz and Nadler’s fixed point theorem and the non-linear alternative for Kakutani maps in showing the existence results for a tripled system of sequential fractional differential inclusions.
Preliminaries are introduced in the second section, main results are shown in the third section. Finally, in
Section 4, we give some numerical examples to show the effectiveness of the obtained theoretical results.
2. Preliminaries
This portion introduces basic fractional calculus concepts, definitions, and tentative results [
1,
2,
3].
Let be a Banach space endowed with the norm . Then is also a Banach space equipped with the norm
Let be a normed space and that , .
A multi-valued map is
- (a)
Convex valued if is convex ;
- (b)
Upper semi-continuous (U.S.C.) on if, for each ; the set is a non-empty closed subset of and if, for each open set of containing , there exists an open neighborhood of , such that ;
- (c)
Lower semi-continuous (L.S.C.) if the set is open for any open set in ;
- (d)
Completely continuous (C.C) if is relatively compact (r.c) for every .
A map of multi-valued is said to be measurable if, for every , the function is measurable.
A multi-valued map is said to be Caratheodory if
- (i)
is measurable for each ;
- (ii)
is U.S.C for almost all .
Further, a Caratheodory function is called -Caratheodory if
- (i)
For each , ∃∋ with and for a.e. .
Lemma 1. Let a closed convex subset of a Banach space and be an open subset of with . In addition, is an u.s.c compact map. Then either
has fixed point in or
∃ and , such that .
Lemma 2 ([
29]).
Let be a completely continuous operator in Banach Space and the set is bounded. Then has a fixed point in . Definition 1. The fractional integral of order ψ with the lower limit zero for a function k is defined asprovided the right-hand side is point-wise defined on , where is the gamma function, which is defined by Definition 2. The R-L fractional derivative of order is defined aswhere the function k has absolutely continuous derivative up to order . Definition 3. The Caputo derivative of order for a function can be written as Note that the CFDs of order almost everywhere on if .
Next, we state and prove the auxiliary lemma, which will help us in constructing the existence results for our proposed system.
Lemma 3. Let and . Then the solution of the linear fractional differential system,is given by 3. Multi-Valued System
Definition 4. A function satisfying the boundary conditions and for which there , such that
a.e. on and
With the help of Lemma 3, we define an operator
by
and
For easy calculations, we set
Next, we define the operators as follows:
Then, we define an operator
by
and
3.1. The Caratheodory Case
Our first result dealing with convex values , and is proved via the Leray–Schauder non-linear alternative for multi-valued maps.
Theorem 1. Suppose that the following conditions are satisfied:
are Caratheodory and have convex values;
There exist continuous non-decreasing functions functions , such thatandfor each ; there exists a number , such thatwhere and are given by (10). The tripled system has at least one solution on . Proof. Consider the operator
defined by (
11)–(
13). From
, it follows that sets
,
and
are non-empty for each
. Then, for
for
, we have
and
and
where
, and
.
For the applicability of Leray–Schauder non-linear alternative we split our proof into several steps.
Claim 1. The operator
is convex. Let
Then there exist
such that, for each
, we have
and
Let
. Then, for each
, we have
and
We deduce that and are convex valued, since are convex valued. obviously, ,, and hence .
Claim 2. We show that the operator
maps bounded sets into bounded sets in
. Let
, define
be a bounded set in
. Then, there exist
and
, such that
Claim 3. We show the equi-continuity of the operator
. Let
with
. Then there exist
,
, and
, such that
and,
Therefore, the operator is equi-continuous, based on Arzela–Ascoli is completely continuous. We know that a completely continuous operator is upper semi-continuous if it has a closed graph. Thus, we need to prove that has a closed graph.
Claim 4. We show that the operator
has closed graph. As it is known that a completely continuous operator is upper semi-continuous if it has a closed graph. For this we take
,
and
, then we need to show
. Observe that
implies that exist
,
, and
such that
and
Let us consider the continuous linear operator
given by
and
and
From, we know that
is closed graph operator. Further, we have
for all
n. Since
,
it follows that
and
, and
, such that
and
that is,
.
Exists with: let
. this implies that the function
,
, and
exists with:
and
following the same arguments
which implies that
In the light of
we can find
with
. Consider
Here, is completely continuous and upper semi-continuous. There is no for some depending on choosing of .
So, by the non-linear alternative of Leray–Schauder type, we conclude that
has it least one fixed point
, this solution of problem (
1). By this, we finalize the proof. □
3.2. The Case of Libschitz
Here, we consider the situation where there are non-convex values in the multi valued maps of system (
1).
Consider the metric space which is induced from the normed space , and consider be given by where and
So is a metric space and is a generalized one.
In the upcoming result, we take advantage of Covitz and Nadler’s fixed point theorem for multi-valued maps.
Theorem 2. are such that , , and are measurable for each
andfor the majority of and with and for almost hold, this implies the existence of solution for system (1) on given that Proof. The sets , and are non-empty for each by assumption , so , and have measurable selections. We now demonstrate that the operator meets the criteria of Covitz and Nadler’s fixed point theorem.
We start by
for each
. Let
, such that
in
. Then
and there exists
,
, and
, such that
and
because of the compact values
,
, and
, we take the sub-sequences to show that
,
and
tends to
,
, and
in
, respectively. Thus,
,
, and
for each
and that
and
So
, which guarantees that
is closed. After that, we prove the existence of
, such that
Let
and
then there exist
,
, and
such that, ∀
, this gives
So, there
,
and
such that
and
Defined
by
and
Since the multi-valued operators
,
and
are measurable, there exist functions
which are a measurable selection for
and
,
,
such that, for a.e.
, we have
and
Thus
likewise, by reversing the roles of
and
, it is possible to obtain
In light of the assumption,
is a contraction. Therefore, according to Covitz and Nadler’s fixed point theorem, it has a fixed point
that is a solution to problem (
1). This concludes the proof. □