Abstract
This research investigates the dynamics of higher-order nonlinear difference equations, specifically concentrating on seventh-order instances. Analytical solutions are obtained for particular equations, a formidable task owing to the absence of explicit mathematical techniques for their resolution. The qualitative characteristics of solutions, such as their stability, boundedness, and periodicity, are analysed by theoretical methods and numerical simulations. The results indicate that equilibrium points frequently lack local asymptotic stability, leading to intricate phenomena such as unbounded solutions and periodic attractors. These findings augment our understanding of nonlinear difference equations, offering significant implications for their use across various scientific fields.
MSC:
39A05; 39A22; 39A23; 39A30
1. Introduction
Recently, difference equations have been considered one of the most used equations for modeling phenomena. Since difference equations have many features to provide more accurate predictions, scientists tend to use them in their models in different fields of research, such as population dynamics and genetics in biology, hypergeometric Poisson distributions in probability problems, etc. However, there are two ways to study difference equations. The first is by analyzing the qualitative behavior of solutions, for example, investigating the solutions’ stability, boundedness, and periodicity. So, several articles have been published for studying rational difference equations in this case, for instance, the following recent studies:
Kerker et al. [1] discussed boundedness and global solutions. Also, an oscillation result for positive solutions was obtained for the higher-order non-autonomous difference equation
In [2], the local and global stability and periodicity were examined in the fourth-order nonlinear difference equation
Garic-Demirovic et al. [3] investigated the bifurcation of a fixed point in a special case involving complex conjugate numbers and the local stability and global attractivity of period-two solutions of a homogeneous fractional difference equation and the unique equilibrium point of
The second method is to obtain the form of solutions, which is more challenging for researchers since there is no explicit mathematical method for solving nonlinear difference equations. Therefore, there exists a great interest in studying difference equations by structuring the solutions’ forms. Some recent papers are presented as follows:
Tollu et al. [4] derived a closed-form solution and analyzed the asymptotic behavior of the solutions to the nonlinear difference equation
El-Metwally et al. [5] looked into some of the qualitative behavior of the solutions such as the the global stability, boundedness, and periodicity characteristic for rational recursive sequences:
Jia [6] investigated the equilibrium point’s asymptotic stability, as well as establishing criteria for the solution’s positivity for the following high-order fuzzy difference equation:
Kara et al. [7] explored the closed-form solution and discussed the dynamics of some cases of the following system:
For additional research in this area, we direct the reader to [8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31] and the sources listed therein.
In this paper, we modified [5] to a seventh-order nonlinear difference equation and derived explicit solutions to some cases of difference equations, which are listed below and whose analytical solutions are usually a major challenge for researchers. In addition, a comprehensive analysis of the qualitative properties of the solutions, such as their stability, boundedness, and periodicity, is provided through both the theoretical results and numerical simulations.
where the initial values for are arbitrary real numbers.
This paper is arranged as follows: In Section 2, we recall some fundamental definitions and theorems from difference equations. Section 3 is designed to discuss the dynamics of the first case of (1). In Section 4, we illustrate the explicit solution and investigate the periodic behavior of the second case of (1). Section 5 and Section 6 contain the results for the last two cases of (1). We provide some numerical simulations in Section 7. The discussion about the findings is given in Section 8.
2. Definitions and Fundamental Theorems
In this phase, we review certain concepts and conclusions from the theory of difference equations that will be utilized in our investigation. Suppose J is a continuously differentiable function such that , where is a real number interval and k is a positive integer. Then, the difference equation
has a unique solution for all sets of inital values [32].
Definition 1.
Definition 2.
The equilibrium point of Equation (2) is said to be
- Locally stable if, for every , there exists such that for every , withwe have
- Locally asymptotically stable if is a locally stable solution of Equation (2) and there exists such that for every , withwe have
- A global attractor if, for every , we have
- Globally asymptotically stable if is locally stable and also a global attractor of Equation (2).
- Unstable if is not a locally stable solution of Equation (2).
Definition 3.
A sequence is a periodic solution with a period q if for all .
Theorem 1
(Kocic and Ladas [33]). Assume that , where and . Then,
is a sufficient condition for the asymptotic stability of the following difference equation
3. The First Case
This section discusses the equilibrium point and the state of stability. Also, a specific form of solution will be clarified for the following difference equation:
where the initial values are arbitrary real numbers.
Theorem 2.
The equilibrium point of difference Equation (3) has a unique zero value.
Proof.
Theorem 3.
The equilibrium point of difference Equation (3) is not locally asymptotically stable.
Proof.
Suppose that is a function defined as follows:
After differentiating with respect to , , , , , , and , we obtain
Now, by substituting into for , we obtain
Form of Solution
The solution of Equation (3) is obtained in a specific form.
Theorem 4.
Assume is a solution of (3) and suppose that , , , , , , and .
Proof.
It is clear that for , the result is true. Now for , assume the result holds for and it is given as follows:
Now, the first relation will be proven.
After substituting into Equation (3), we obtain
Substituting in the values of , and gives
so
Consequently,
Similarly, we can prove the second form.
From Equation (3), we see that
which implies that
i.e,
Thus,
The remaining forms can be verified using the same approach. The proof is complete. □
4. The Second Case
The calculation of equilibrium points and their state of stability is shown in this part for the following difference equation:
where the initial values are arbitrary non-zero real numbers with and .
Theorem 5.
Difference Equation (8) has three equilibrium points , which are 0 and .
Proof.
Theorem 6.
The equilibrium points of difference Equation (8) are not locally asymptotically stable.
Proof.
Suppose that is a function defined as follows:
After differentiating with respect to , , , , , , and , we obtain
Now, substituting into for , we obtain
Hence, the linearized equation of (8) about the equilibrium points is
Therefore, we find that the equilibrium points of Equation (8) are not locally stable using Theorem 1. The proof is complete. □
Form of Solution
In this part, the form of the solution to the difference Equation (8) is demonstrated.
Theorem 7.
Proof.
It is clear that at , the result is true. Now, for , assume the result is true at and it is given as follows:
Now, the first form will be established.
Substituting into Equation (8), we obtain
Substituting in the values of and gives
so
Likewise, we can prove the second form.
It follows from Equation (8) that
which implies that
Consequently,
Similarly, the remaining forms can be proven. The proof is complete. □
Theorem 8.
Difference Equation (8) has a periodic solution of period six if and and will take the form .
Proof.
Suppose that there exists a prime period-six solution to the difference Equation (8). Then, we can recognize from the form of the solution of Equation (8) that
So
Then, assume that and . Consequently, we see from the form of the solution to Equation (8) that
Therefore, we have a periodic solution of period six. The proof is complete. □
Theorem 9.
The solution of difference Equation (8) is unbounded if and .
Proof.
The proof, in this case, directly follows the form of the solution, as given in Theorem 7. □
5. The Third Case
We illustrate the state of stability of the equilibrium point, the form of the solutions, and the numerical simulation of the following difference equation:
where the initial values are arbitrary positive real numbers.
Theorem 10.
Difference Equation (13) has a unique equilibrium point , which is the number zero and is not locally asymptotically stable.
Proof.
See proofs of Theorems 2 and 3. □
Theorem 11.
Proof.
We leave this to the readers, and it can be proven by using the same approach as for Theorem 4. □
6. The Fourth Case
The state of the stability of the equilibrium point, a specific form of solution, and numerical examples will be presented for the following difference equation:
where the initial values are arbitrary non-zero real numbers with and .
The following theorems can be proven by using the same approach as for the previous theorems given in Section 4, and we leave this to the readers.
Theorem 12.
Difference Equation (14) has a unique equilibrium point , and this equilibrium point is not locally asymptotically stable.
Theorem 13.
Theorem 14.
Difference Equation (14) has a periodic solution of period six if and and will take the form .
Theorem 15.
The solutions of difference Equation (14) are unbounded if and .
7. Numerical Results
In this section, we provide some numerical simulations that support the above theoretical results.
Example 1.
Figure 1 illustrates that the behavior of difference Equation (3) is unstable in response to the random values , , , , , , and .
Figure 1.
Dynamic behavior of Equation (3).
Example 2.
Figure 2 shows that the solution of Equation (8) is unbounded when the initial values are , , , , , , and .
Figure 2.
Dynamic behavior of Equation (8).
Example 3.
Consider Equation (10) under the initial conditions , , , , , , and ; then, Figure 3 represents a periodic solution of period six.
Figure 3.
Dynamic behavior of Equation (10).
Example 4.
Figure 4 shows the numerical solution of difference Equation (13) with initial values of , , , , , , and .
Figure 4.
Dynamic behavior of Equation (13).
Example 5.
Meanwhile, in Figure 5, the different behavior of solutions for (13) is presented with the following random initial values: , , , , , , and .
Figure 5.
Dynamic behavior of Equation (13).
8. Conclusions
This research examines the solutions and qualitative theory of many higher-order nonlinear difference equations, focusing primarily on their stability, boundedness, and periodicity. Through theoretical methodologies and numerical simulations, we derived explicit solutions for some cases of Equation (1). The results indicate that for these equations, equilibrium points are typically not locally asymptotically stable, leading to chaos, namely, the coexistence of stable unbounded and periodic attractors. Consequently, these findings augment our understanding of nonlinear difference equations, which will be beneficial for their application in mathematical modeling across several scientific disciplines. Future research may focus on applying these methods to other unresolved difference equations and exploring potentially more universal solutions.
Author Contributions
Methodology, T.D.A. and M.R.H.; software, T.D.A.; formal analysis, T.D.A. and M.R.H.; writing, review and editing, T.D.A. and M.R.H. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Data Availability Statement
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
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