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Monotone iterative solutions for a coupled system of p-Laplacian differential equations involving the Riemann–Liouville fractional derivative
Advances in Difference Equations volume 2021, Article number: 103 (2021)
Abstract
Applying the monotone iterative technique and the method of upper and lower solutions, we investigate the existence of extremal solutions for a nonlinear system of p-Laplacian differential equations with nonlocal coupled integral boundary conditions. We present a numerical example to illustrate the main result.
1 Introduction
Consider the following fractional differential system with the nonlocal coupled integral boundary conditions:
where \(D^{\alpha }\) and \(D^{\beta }\) are the standard Riemann–Liouville fractional derivatives, \(I^{\sigma }\) and \(I^{\omega }\) are the Riemann–Liouville fractional integrals, and \(1<\alpha , \beta <2\), \(\sigma ,\omega >1\), \(0<\eta ,\xi <1\), \(a_{1},a_{2},d_{1},d_{2}\in \mathbb{R}\), \(a_{2}\geq a_{1}\), \(d_{2}\geq d_{1}\), \(f,g\in C([0,1]\times \mathbb{R}\times \mathbb{R},\mathbb{R})\), \(h,k\in C([0,1]\times \mathbb{R},\mathbb{R})\). The p-Laplacian operator is defined as \(\phi _{p}(t)=|t|^{p-2}t\), \(p>1\), and \((\phi _{p})^{-1}=\phi _{q}\), \(\frac{1}{p}+\frac{1}{q}=1\).
Fractional differential equations have recently gained much attention. In particular, much effort has been made toward the study of the existence of solutions for fractional differential equations with p-Laplacian operator [1–8]. The monotone iterative technique, combined with the method of upper and lower solutions, is a powerful tool for proving the existence of solutions of nonlinear differential equations; see [9, 10] and the references therein. However, only a few papers considered the upper an lower solutions method and the monotone iteration technique for p-Laplacian boundary value problems with fractional coupled systems. The purpose of this paper is developing a monotone iterative technique to show the existence of an extremal solution for the nonlinear system (1.1) with nonlocal integral boundary conditions.
The paper is organized as follows. In Sect. 2, we give sufficient conditions guaranteeing that (1.1) has an extremal solution and discuss some comparison results, which play a key role in establishing the proposed work. In Sect. 3, we give the main result. Finally, we present an example illustrating our results.
2 Preliminaries
In this section, we introduce definitions and some useful lemmas which play an important role in obtaining the main results of this paper.
Denote
It is a Banach spaces with the norm \(\|u\|_{\alpha }=\|u\|+\|D^{\alpha }u\|\), where \(\|u\|=\max_{0\leq t\leq 1}|u(t)|\) and \(\|D^{\alpha }u\|=\max_{0\leq t\leq 1}|D^{\alpha }u(t)|\).
We need the following assumptions.
\((H_{1})\) There exist \(x_{0},y_{0}\in C_{\alpha }[0,1]\) satisfying \(D^{\beta }(\phi _{p}(-D^{\alpha }x_{0}(t))), D^{\beta }(\phi _{p}(-D^{ \alpha }y_{0}(t)))\in C[0,1]\), \(x_{0}(t)\leq y_{0}(t)\), and \(D^{\alpha }y_{0}(t)\leq D^{\alpha }x_{0}(t)\) such that
\((H_{2})\) There exist two constants \(M, N\in \mathbb{R}\), \(M\geq N\), such that
where \(x_{0}(t)\leq \overline{x(t)}\leq x(t)\leq y_{0}(t)\), \(x_{0}(t)\leq y(t)\leq \overline{y(t)}\leq y_{0}(t)\), and
for \(x_{0}(t)\leq x(t)\leq y(t)\leq y_{0}(t)\).
\((H_{3})\) There exists a constant \(\lambda \geq 0\) such that
where \(x_{0}(t)\leq x(t)\leq y(t) \leq y_{0}(t)\), \(D^{\alpha } y_{0}(t)\leq D^{ \alpha }y(t)\leq D^{\alpha } x(t)\leq D^{\alpha } x_{0}(t)\), \(t\in [0,1]\), and
for \(x_{0}(t)\leq x(t)\leq y(t) \leq y_{0}(t)\), \(D^{\alpha } y_{0}(t)\leq D^{ \alpha }y(t)\leq D^{\alpha } x(t)\leq D^{\alpha } x_{0}(t)\), \(t\in [0,1]\).
\((H_{4})\) \(\Gamma (\beta +\sigma )>\lambda \eta ^{\beta +\sigma -1}\).
\((H_{5})\) \(2\Gamma (\beta +\sigma ) (M+N)<\Gamma (\beta )[\Gamma (\beta + \sigma )-\lambda \eta ^{\beta +\sigma -1}]\).
\((H_{6})\) For any \(t\in (0,1)\), we have
Lemma 2.1
([11])
Let \(h\in C[0,1]\), \(b\in \mathbb{R}\), and \(\Gamma (\beta +\sigma )\neq \lambda \eta ^{\beta +\sigma -1} \). Then the fractional boundary value problem
has the following integral representation of the solution:
where
and \(\Delta =\Gamma (\beta )[\Gamma (\beta +\sigma )-\lambda \eta ^{ \beta +\sigma -1}]\).
Lemma 2.2
([11])
Let \(M, b\in \mathbb{R}\), \(h(t)\in C[0,1]\), \(2\Gamma (\beta +\sigma ) |M|<\Gamma (\beta )[\Gamma (\beta +\sigma )- \lambda \eta ^{\beta +\sigma -1}]\), and \((H_{4})\) hold. Then
has a unique solution \(w(t)\in C[0,1]\).
Lemma 2.3
([10, Lemma 2.4])
Let \(z(t)\in C[0,1]\) and \(l\in \mathbb{R}\). Then the fractional value boundary problem
is equivalent to
where
Lemma 2.4
Assume that \(1<\alpha , \beta <2\), \(\sigma _{1}, \sigma _{2}\in C[0,1]\), M, N are nonnegative constants satisfying \(M\geq N\), and \((H_{4})\) and \((H_{5})\) hold. Then the fractional differential system
has a unique solution in \(C_{\alpha }[0,T]\times C_{\alpha }[0,T]\).
Proof
Let
Using (2.3), we have that
and
Since M, N are nonnegative constants and \(M\geq N\), by assumption \((H_{5})\) we see that
By (2.6) and Lemma 2.2 we know that (2.4) and (2.5) have a unique solution. In consequence, \(\phi _{p}(-D^{\alpha }x(t))\) and \(\phi _{p}(-D^{\alpha }y(t)))\) are also unique, that is,
Then
In view of the boundary value condition (2.3), we obtain
Let
Using (2.7), we have
and
By Lemma 2.3 we know that both (2.8) and (2.9) have a unique solution. In consequence, x and y are also unique. □
Lemma 2.5
([9, Lemma 2.6])
Let M be nonnegative constant, and let \((H_{6})\) hold. If \(w(t)\in C[0,1]\) satisfies \(D^{\beta }w(t)\in C[0,1]\) and
then \(w(t)\geq 0\) for all \(t\in [0,1]\).
Lemma 2.6
([10, Lemma 2.7])
If \(x(t)\in C[0,1]\) satisfies
then \(x(t)\geq 0\) for all \(t \in [0,1]\).
Lemma 2.7
Let M, N be nonnegative constants and \(M\geq N\). If \(u,v\in C[0,1]\) satisfy \(D^{\beta }u(t), D^{\beta }v(t)\in C[0,1]\), and
then \(u(t)\geq 0\) and \(v(t)\geq 0\) for all \(t\in [0,1]\).
Proof
Let \(p(t)=u(t)+v(t)\), \(t\in [0,1]\). Then by (2.10) we have
Thus by (2.11) and Lemma 2.5 we have that
Next, we show that \(u(t)\geq 0\) and \(v(t)\geq 0\) for all \(t\in [0,1]\). Using (2.10) and (2.12), we find that
which, in view of (2.13) and Lemma 2.5, yield \(u(t)\geq 0\) for all \(t\in [0,1]\). In a similar way, we can show that \(v(t)\geq 0\) for all \(t\in [0,1]\). □
3 Main results
Theorem 3.1
Suppose that conditions \((H_{1})\)–\((H_{6})\) hold. Then there is an extremal solution \((x^{*},y^{*})\in [x_{0},y_{0}]\times [x_{0},y_{0}]\) of the nonlinear problem (1.1). Moreover, there exist monotone iterative sequences \(\{x_{n}\},\{y_{n}\}\subset [x_{0},y_{0}]\) such that \(x_{n}\rightarrow x^{*}\), \(y_{n}\rightarrow y^{*}\) (\(n\rightarrow \infty \)) uniformly for \(t\in [0,1]\) and
Moreover, we have
where
Proof
For any \(x_{n-1},y_{n-1}\in C_{\alpha }[0,1]\), \(n\geq 1\), we define
Consider (2.3) as follows:
In view of Lemma 2.4, problem (3.1) has a unique solution in \(C_{\alpha }[0,1]\times C_{\alpha }[0,1]\).
Now we show that \(\{x_{n}(t)\}\) and \(\{y_{n}(t)\}\) satisfy the relations
Let \(u(t)=\phi _{p}(-D^{\alpha }x_{1}(t))-\phi _{p}(-D^{\alpha }x_{0}(t))\), \(v(t)= \phi _{p}(-D^{\alpha }y_{0}(t)) -\phi _{p}(-D^{\alpha }y_{1}(t))\). By condition (3.1) and \((H_{1})\) we have
Also, \(u(0)=0\), and
In a similar way, we can prove that
So, from the above inequality we have
Thus, in view of Lemma 2.7, we get \(\phi _{p}(-D^{\alpha }x_{1}(t))\geq \phi _{p}(-D^{\alpha }x_{0}(t))\), \(\phi _{p}(-D^{\alpha }y_{0}(t)) \geq [4] \phi _{p}(-D^{\alpha }y_{1}(t))\) for all \(t\in [0,1]\). Since \(\Phi _{p}(x)\) is nondecreasing, we have \(D^{\alpha }x_{1}(t)\leq D^{\alpha }x_{0}(t)\) and \(D^{\alpha }y_{0}(t)\leq D^{\alpha }y_{1}(t)\) for all \(t\in [0,1]\).
Let \(\epsilon (t)=x_{1}(t)-x_{0}(t)\), \(\theta (t)=y_{0}(t)-y_{1}(t)\). From (3.1) and \((H_{1})\) we have
and
By Lemma 2.6 we have \(x_{1}(t)\geq x_{0}(t)\) and \(y_{0}(t)\geq y_{1}(t)\) for all \(t\in [0,1]\).
Now we put \(w(t)=\phi _{p}(-D^{\alpha }y_{1}(t))-\phi _{p}(-D^{\alpha }x_{1}(t))\). Applying \((H_{2})\), \((H_{3})\), and (3.1), we obtain
Also, \(w(0)=\phi _{p}(-D^{\alpha }y_{1}(0))-\phi _{p}(-D^{\alpha }x_{1}(0))=0\), and
In view of Lemma 2.5, we have that \(w(t)\geq 0\) for all \(t\in [0,1]\). Thus we have the relation \(\phi _{p}(-D^{\alpha }x_{1}(t))\leq \phi _{p}(-D^{\alpha }y_{1}(t))\), that is, \(D^{\alpha }x_{1}(t)\geq D^{\alpha }y_{1}(t)\), since \(\Phi _{p}(x)\) is nondecreasing. Therefore \(D^{\alpha }y_{0}(t)\leq D^{\alpha }y_{1}(t)\leq D^{\alpha }x_{1}(t) \leq D^{\alpha }x_{0}(t)\) for all \(t\in [0,1]\).
Let \(\delta (t)=y_{1}(t)-x_{1}(t)\). It follows from (3.1) that
By Lemma 2.6 we obtain \(y_{1}(t)\geq x_{1}(t)\) for all \(t\in [0,1]\). Hence we have the relation \(x_{0}(t)\leq x_{1}(t)\leq y_{1}(t)\leq y_{0}(t)\).
Now we assume that
We will prove that (3.2) is also true for \(k+1\). Let
By \((H_{2})\), \((H_{3})\), and (3.1) we have that
and
In view of Lemmas 2.5–2.7, we obtain
From the above, by induction, it is not difficult to prove that \(x_{0}\leq x_{1}\leq \cdots \leq x_{n}\leq \cdots \leq y_{n}\leq \cdots \leq y_{1}\leq y_{0}\) and \(D^{\alpha } y_{0}\leq D^{\alpha } y_{1}\leq \cdots \leq D^{\alpha } y_{n} \leq \cdots \leq D^{\alpha } x_{n}\leq \cdots \leq D^{\alpha } x_{1} \leq D^{\alpha } x_{0}\).
Since the solution space is \(C_{\alpha }[0,1]\), the sequences \(\{x_{n}\}\) and \(\{y_{n}\}\) are uniformly bounded and equicontinuous. The Arzelà–Ascoli theorem guarantees that they are relatively compact sets in the space \(C_{\alpha }[0,1]\). Therefore \(\{x_{n}\}\) and \(\{y_{n}\}\) converge to \(x^{*}(t)\) and \(y^{*}(t)\) uniformly on \([0,1]\), respectively, that is,
and
uniformly in \(t\in [0,1]\). Moreover, from (3.1) and (3.2) we obtain that \(x^{*}(t)\) and \(y^{*}(t)\) are solutions of problem (1.1).
Finally, we show that \((x^{*},y^{*})\) is an extremal solution of system (1.1). Let \((x,y)\in [x_{0},y_{0}]\times [x_{0},y_{0}]\) be any solution of problem (1.1), that is,
Applying (3.1), (3.5), \((H_{2})\), \((H_{3})\), Lemma 2.6, and Lemma 2.7, we have
Taking the limit as \(n\rightarrow \infty \) in (3.6), we have \(x^{*}\leq x\), \(y\leq y^{*}\), that is, \((x^{*}, y^{*})\) is an extremal solution of system (1.1) in \([x_{0},y_{0}]\times [x_{0},y_{0}]\). This completes the proof. □
4 Iteration procedure and a numerical example
In this section, we introduce a numerical procedure to obtain an appropriate solution of (1.1). Define
For the iteration Eq. (3.1), let \(\phi _{p}(-D^{\alpha }x_{n}(t))=u_{n}\). Then \(-D^{\alpha }x_{n}(t)=\phi _{q}(u_{n})\), and with the boundary conditions \(x_{n}(0)=0\) and \(D^{\alpha -1}x_{n}(1)=D^{\frac{2}{3}}x_{n}(1)=I^{\omega }x_{n-1}(\xi )+d_{1}=l_{1}\), by Lemma 2.3 we have
where \(l_{1}=\frac{1}{\Gamma (\omega )}\int _{0}^{\xi }(\xi -s)^{\omega -1}x_{n-1}(s)\,ds+d_{1}\) and
We can also put \(\phi _{p}(-D^{\alpha }y_{n}(t))=v_{n}\). Then \(-D^{\alpha }y_{n}(t)=\phi _{q}(v_{n})\). In a similar way, we can prove that
where \(l_{2}=\frac{1}{\Gamma (\omega )}\int _{0}^{\xi }(\xi -s)^{\omega -1}y_{n-1}(s)\,ds+d_{2}=1.1284 \int _{0}^{\frac{1}{2}}(\frac{1}{2}-s)^{\frac{1}{2}}y_{n-1}(s)\,ds+0.004\). Thus the iteration Eq. (3.1) can be rewritten as
Applying Lemma 2.1 to (4.3), we obtain
where \(b_{1}= I^{\sigma }h(\eta ,u_{n-1}(\eta )) -\lambda I^{\sigma }u_{n-1}( \eta )+a_{1}\), \(b_{2}= I^{\sigma }k(\eta ,v_{n-1}(\eta )) -\lambda I^{\sigma }v_{n-1}( \eta )+a_{2}\), and
\(\Delta =\Gamma (\beta )[\Gamma (\beta +\sigma )-\lambda \eta ^{ \beta +\sigma -1}]\).
Discretize the interval \([0,1]\) with the nodes \(t_{i}=ih\), \(h=\frac{1}{K}\), \(K\in \mathbb{N}\). Let \(x_{n}^{(i)}\approx x_{n}(t_{i})\), \(u_{n}^{(i)}\approx u_{n}(t_{i})\), \(H(i,j)=H(t_{i},s_{j})\), \(G(i,j)=G(t_{i},s_{j})\), and
Using the trapezoidal quadrature rule to approximate the integrals in the right-hand sides of (4.4), (4.2), and (4.1), we obtain the following linear systems of equations:
and
for the unknown \(u_{n}^{(i)}\), \(x_{n}^{(i)}\), \(0\leq i\leq K\), where \(\{d_{j}\}\) are the coefficients in the rule, \(d_{0}=d_{K}=1\), and \(d_{j}=2\) for \(1\leq j\leq K-1\).
Setting \(G_{ij}=\frac{h}{2}\sum_{j=0}^{K}G(i,j)d_{j}\), \(H_{ij}=\frac{h}{2}\sum_{j=0}^{K}H(i,j)d_{j}\), the matrix \(\Phi =(G_{ij})\), and \(B=(H_{ij})\) with the identity matrix \(\mathbb{I}\). Systems (4.5) and (4.6) can be written as a system of matrix–vector equations
where \(\overrightarrow{X}_{n}=[{x}_{n}^{(0)},{x}_{n}^{(1)},\ldots ,{x}_{n}^{(K)}] \), \(\overrightarrow{Y}_{n}=[{y}_{n}^{(0)},{y}_{n}^{(1)},\ldots ,{y}_{n}^{(K)}]\), \(\overrightarrow{U}_{n}=[{u}_{n}^{(0)},{u}_{n}^{(1)},\ldots ,{u}_{n}^{(K)}]\), \(\overrightarrow{V}_{n}=[{v}_{n}^{(0)},{v}_{n}^{(1)},\ldots ,{v}_{n}^{(K)}]\), \(S=[t_{0},t_{1},\ldots ,t_{K}]^{T}\), and \(\overrightarrow{F}_{n-1}\), \(\overrightarrow{G}_{n-1}\) are column vectors of their components \(F_{n-1}^{(i)}=\frac{h}{2}\sum_{j=0}^{K}G(i,j)d_{j}f_{n-1}^{(j)}\), \(G_{n-1}^{(i)}=\frac{h}{2}\sum_{j=0}^{K}G(i,j)d_{j}g_{n-1}^{(j)}\).
Example 4.1
Consider the following problem:
where \(\beta =\frac{7}{4}\), \(\alpha =\frac{5}{3}\), \(\sigma =\frac{5}{4}\), \(\omega =\frac{3}{2}\), \(\eta =\frac{1}{4} \), \(\xi =\frac{1}{2}\), \(a_{1}=0.1\), \(a_{2}=0.2\), \(d_{1}=0.003\), \(d_{2}=0.004\), \(p=4\), and
Take \(x_{0}(t)=0\) and \(y_{0}(t)=3t^{\frac{2}{3}}- \frac{9\Gamma (\frac{2}{3})}{14\Gamma (\frac{1}{3})}t^{\frac{7}{3}}\). Then \(-1\leq -t^{\frac{2}{3}}=D^{\frac{5}{3}}y_{0}(t)\leq D^{\frac{5}{3}}x_{0}(t)=0\). It is not difficult to verify that \((H_{1})\) holds.
Since the function \(\sqrt[3]{x}+x^{3}\) is increasing for \(x\in R\), we obtain
where \(x_{0}(t)\leq \overline{x(t)}\leq x(t)\leq y_{0}(t)\), \(x_{0}(t)\leq y(t)\leq \overline{y(t)}\leq y_{0}(t)\), and \(x_{0}(t)\leq x(t)\leq y(t)\leq y_{0}(t)\). Thus \((H_{2})\) and \((H_{3})\) hold. From (4.9) and (4.10) we have \(M=\frac{1}{6}\sqrt[3]{3}\), \(N=0\), and \(\lambda =1\). Then
which show that \((H_{4})\), \((H_{5})\), and \((H_{6})\) hold. Thus all conditions of Theorem 3.1 are satisfied. In consequence, the nonlinear system (4.8) has an extremal solution \((x^{*},y^{*})\in [x_{0}(t),y_{0}(t)]\times [x_{0}(t),y_{0}(t)]\). Moreover, for this example, we found that for \(\delta =10^{-10}\), which took \(N=16\) iterations for \(E(N)<\delta \). The graphs of \({x_{n}}\) and \({y_{n}}\) for some values of n are shown in Table 1 and Fig. 1.
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References
Zhang, X., Liu, L., Wiwatannapataphee, B., Wu, Y.: The eigenvalue for a class of singular p-Laplacian fractional differential equations involving the Riemann–Stieltjes integral boundary condition. Appl. Math. Comput. 235, 412–422 (2014)
Lu, H., Han, Z., Sun, S.: Multiplicity of positive solutions for Sturm–Liouville boundary value problems of fractional differential equations with p-Laplacian. Bound. Value Probl. 26, 1–17 (2014)
Li, S., Zhang, X., Wu, Y., Caccetta, L.: Extremal solutions for p-Laplacian differential systems via iterative computation. Appl. Math. Lett. 26, 1151–1158 (2013)
Jiang, W.: Solvability of fractional differential equations with p-Laplacian at resonance. Appl. Math. Comput. 260, 48–56 (2015)
Zhang, X., Liu, L., Wu, Y., Lu, Y.: The iterative solutions for nonlinear factional differential equation. Appl. Math. Comput. 219, 4680–4691 (2013)
Zhang, X., Han, Y.: Existence and uniqueness of positive solutions for higher order nonlocal fractional differential equations. Appl. Math. Lett. 25, 555–560 (2012)
Li, Y., Lin, S.: Positive solutions for the nonlinear Hadamard type fractional differential equations with p-Laplacian. J. Funct. Spaces Appl. 2013, Art. 951643 (2013)
Han, Z., Lu, H., Zhang, C.: Positive solutions for eigenvalue problems for fractional differential equation with generalized p-Laplacian. Appl. Math. Comput. 257, 526–536 (2015)
He, Y.: Existence results and the monotone iterative technique for nonlinear fractional differential systems involving fractional integral boundary conditions. Adv. Differ. Equ. 2017, 264 (2017)
He, Y., Bi, B.: Existence and iteration of positive solution for fractional integral boundary value problems with p-Laplacian operator. Adv. Differ. Equ. 2019, 415 (2019)
Wang, G.: Explicit iteration and unbounded solutions for fractional integral boundary value problem on an infinite interval. Appl. Math. Lett. 47, 1–7 (2015)
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The authors sincerely thanks the editor and reviewers for their valuable suggestions and useful comments to improve the manuscript.
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This work is supported by Scientific Research Foundation of Hainan Medical University (No. 2020030).
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Bi, B., He, Y. Monotone iterative solutions for a coupled system of p-Laplacian differential equations involving the Riemann–Liouville fractional derivative. Adv Differ Equ 2021, 103 (2021). https://doi.org/10.1186/s13662-020-03203-w
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DOI: https://doi.org/10.1186/s13662-020-03203-w