Electronic Journal of Differential Equations, Vol. 2024 (2024), No. 38, pp. 1–12. ISSN: 1072-6691. URL: https://ejde.math.txstate.edu, https://ejde.math.unt.edu DOI: 10.58997/ejde.2024.38 A SECOND ORDER CONVERGENT DIFFERENCE SCHEME FOR THE INITIAL-BOUNDARY VALUE PROBLEM OF ROSENAU-BURGERS EQUATION SITONG DONG, XIN ZHANG, YUANFENG JIN Abstract. We construct a two-level implicit nonlinear finite difference scheme for the initial boundary value problem of Rosenau-Burgers equation based on the method of order reduction. We discuss conservation, unique solvability, and convergence for the difference scheme. The new scheme is shown to be second-order convergent in time and space. Finally, numerical simulations illustrate our theoretical analysis. 1. Introduction In the study of the dynamics of dense discrete systems, the case of wave-wave and wave-wall interactions cannot be described using the well-known KDV equation which was suggested by Korteweg and de Vries in 1895 [1]. To overcome this shortcoming, Rosenau [2, 3] proposed an equation in the form ut + uxxxxt + ux + uux = 0. (1.1) The theoretical results on the existence, uniqueness and regularity of the solutions to (1.1) have been investigated by Park [4]. But it is difficult to find the analytical solution for (1.1). Much attention has devoted to numerical solutions of (1.1) by various numerical methods [5, 6, 7, 8]. On the other hand, for the further consideration of dissipation in space for dy- namic systems, such as the phenomenon of bore propagation and water waves, the viscous term −uxx needs to be included ut + uxxxxt − uxx + ux + uux = 0. (1.2) This equation is usually called the Rosenau–Burgers equation. Many scholars had proposed difference schemes for the Rosenau–Burgers Equation. Hu et al [9] consid- ered a nonlinear Crank-Nicolson difference scheme for the Rosenau-Burgers equa- tion by the Newton iterative algorithm. Pan and Zhang [10] discussed a three-level linear implicit difference scheme for the Rosenau-Burgers equation which is un- conditionally stable. Ahmat and Abduwali [11] investigated two class of modified local Crank- Nicolson schemes for the Rosenau-Burgers equation,which has simple 2020 Mathematics Subject Classification. 65M06, 65M12. Key words and phrases. Rosenau-Burgers equation; nonlinearized difference scheme; conservation law; convergence. ©2024. This work is licensed under a CC BY 4.0 license. Submitted December 2, 2023. Published July 4, 2024. 1 2 S. DONG, X. ZHANG, Y. JIN EJDE-2024/38 structure and high accuracy. Omrani [12] explored the Galerkin–Crank–Nicolson discrete method. Guo et al [13] considered a two-level implicit nonlinear discrete scheme, which preserves the energy decline property of the Rosenau–Burgers equa- tion. Luo et al [14] used a three-level linear implicit finite difference scheme with energy dissipation which has second-order and fourth-order in time and space. For the two-dimensional case, Rouatbi et al [15] presented a linearized Crank–Nicolson difference scheme. In this article, we consider the initial-boundary value problem of the Rosenau- Burgers equation by the finite difference method. ut + uxxxxt − uxx + ux + uux = 0, 0 < x < L, 0 < t ≤ T, (1.3) u(x, 0) = φ(x), 0 ≤ x ≤ L, (1.4) u(0, t) = 0, u(L, t) = 0, uxx(0, t) = 0, uxx(L, t) = 0, 0 ≤ t ≤ T, (1.5) where φ(x) is a given function. The initial-boundary value problem of the Rose- nau–Burgers equation contains at least one derivative boundary condition. There- fore, a difference scheme must be established at the node adjacent to this boundary point that is consistent with the difference schemes on the other nodes. To achieve this, we employ the method of order reduction to get a difference scheme with con- vergence order two in both space and time. Additionally, we rigorously prove the convergence of this particular difference. This article is structured as follows. In Section 2, we introduce some useful notation and lemmas. In Section 3, we describe a conservative two-level implicit nonlinear finite difference scheme for the Rosenau–Burgers equation. The scheme has second-order accuracy in space and time. In Section 4, we analize the unique solvability is analyzed. In Section 5, we prove the convergence and stability for the difference schem. Finally, a numerical example illustrates our theoretical results. 2. Preliminaries In this section, we introduce notation and lemmas that will be used throughout this article. To partition the domain [0, L] × [0, T ], we use positive integers M and N . Let h = L/M and τ = T/N . Denote xi = ih, 0 ≤ i ≤ M ; tk = kτ , 0 ≤ k ≤ N ;Ωh = {xi : 0 ≤ i ≤ M}, Ωτ = {tk : 0 ≤ k ≤ N}, Ωhτ = Ωh × Ωτ . For each grid function v = {vki : 0 ≤ i ≤M, 0 ≤ k ≤ N} defined on Ωhτ , we denote δ+x v k i = 1 h (vki+1 − vki ), δ 2 xv k i = 1 h (δ+x v k i − δ+x v k i−1),∆xv k i = 1 2h (vki+1 − vki−1), v k+ 1 2 i = 1 2 (vki + vk+1 i ), vki+ 1 2 = 1 2 (vki + vki+1), δtv k+ 1 2 i = 1 τ (vk+1 i − vki ), Let Vh = {v : v = (v0, v1, . . . , vM−1, vM )} and V̊h = {v : v ∈ Vh, v0 = vM = 0} be the spaces of grid functions on Ωh. For any grid functions u, v ∈ Vh, we define the discrete inner product (u, v) = h M−1∑ i=1 uivi, and the corresponding norms (seminorm) ∥u∥ = √ (u, u), |u|1 = √ (δ+x u, δ + x u), ∥u∥∞ = max 1≤i≤M |ui| EJDE-2024/38 A DIFFERENCE SCHEME FOR ROSENAU-BURGERS EQUATION 3 In addition, we define the function ψ(u, v)i = 1 3 [ui∆xvi +∆x(uv)i], 1 ≤ i ≤M. Lemma 2.1 ([16]). For each grid function u, v ∈ V̊h, we have ∥v∥∞ ≤ √ L 2 |v|1, |v|1 ≤ 2 h ∥v∥, ∥v∥ ≤ L√ 6 |v|1, (δ2xu, v) = −(δ+x u, δ + x v). And for an arbitrary ε > 0, we have ∥v∥2∞ ≤ ε|v|21 + 1 4ε ∥v∥2. Lemma 2.2 ([17]). For each grid functions u ∈ Vh and v ∈ V̊h we have (ψ(u, v), v) = 0, (∆xu, u) = 0. Lemma 2.3 (Gronwall inequality [17]). Let {F k}∞i=0 and {gk}∞i=0 be two non- negative sequences and satisfy F k+1 ≤ (1 + cτ)F k + τgk, k = 0, 1, 2, . . . , then F k ≤ exp(ckτ) ( F 0 + τ k−1∑ l=0 gl ) , k = 0, 1, 2, . . . 3. Nnonlinear conservative difference scheme In this section, we use the method of reduction of order to establish a difference scheme for the problem (1.3)-(1.5), and illustrate the truncation errors in detail, then we analyze the conservation of the difference scheme. 3.1. Construction of difference scheme. Let v = uxx, then problem (1.3)–(1.5) is equivalent to ut + vxxt − v + ux + uux = 0, 0 < x < L, 0 < t ≤ T, (3.1) v = uxx, 0 < x < L, 0 < t ≤ T, (3.2) u(x, 0) = φ(x), 0 < x < L, (3.3) u(0, t) = 0, u(L, t) = 0, uxx(0, t) = 0, uxx(L, t) = 0, 0 ≤ t ≤ T . (3.4) According to (3.1) and (3.4), v(0, t) = 0, v(L, t) = 0, 0 ≤ t ≤ T . (3.5) We define the grid functions U = {Uk i : 0 ≤ i ≤M, 0 ≤ k ≤ N} and V = {V k i : 0 ≤ i ≤M, 0 ≤ k ≤ N}, where Uk i = u(xi, tk) and V k i = v(xi, tk). Considering (3.1) at the point (xi, t k+ 1 2 ) and (3.4) at the point (xi, tk), ut(xi, tk+ 1 2 ) + vxxt(xi, tk+ 1 2 )− v(xi, tk+ 1 2 ) + ux(xi, tk+ 1 2 ) + u(xi, tk+ 1 2 )ux(xi, tk+ 1 2 ) = 0, 1 ≤ i ≤M − 1, 1 ≤ k ≤ N − 1, (3.6) v(xi, tk) = uxx(xi, tk), 1 ≤ i ≤M − 1, 1 ≤ k ≤ N. (3.7) 4 S. DONG, X. ZHANG, Y. JIN EJDE-2024/38 By using the Taylor expansion, δtU k+ 1 2 i + δtδx 2V k+ 1 2 i − V k+ 1 2 i +∆xU k+ 1 2 i + ψ(Uk+ 1 2 , Uk+ 1 2 )i = R k+ 1 2 i , 1 ≤ i ≤M − 1, 0 ≤ k ≤ N − 1, (3.8) V k i = δ2xU k i +Qk i , 1 ≤ i ≤M − 1, 0 ≤ k ≤ N, (3.9) there exist constants c1 and c2 such that |Rk+ 1 2 i | ≤ c1(τ 2 + h2), 1 ≤ i ≤M − 1, 0 ≤ k ≤ N − 1, |Qk i | ≤ c2h 2, 1 ≤ i ≤M − 1, 0 ≤ k ≤ N, |δtQ k+ 1 2 i | ≤ c2(τ 2 + h2), 1 ≤ i ≤M − 1, 0 ≤ k ≤ N − 1. (3.10) Notice that the initial-boundary conditions (3.3)–(3.5) become U0 i = φ(xi), 1 ≤ i ≤M − 1, Uk 0 = 0, Uk M = 0, 0 ≤ k ≤ N, V k 0 = 0, V k M = 0, 0 ≤ k ≤ N. (3.11) Omitting the small terms in (3.8) and (3.9) and combining with (3.11), we can derive the difference scheme for (3.1)-(3.4), δtu k+ 1 2 i + δtδx 2v k+ 1 2 i − v k+ 1 2 i +∆xu k+ 1 2 i + ψ(uk+ 1 2 , uk+ 1 2 )i = 0, 1 ≤ i ≤M − 1, 0 ≤ k ≤ N − 1, (3.12) vki = δ2xu k i , 1 ≤ i ≤M − 1, 0 ≤ k ≤ N, (3.13) u0i = φ(xi), 1 ≤ i ≤M − 1, (3.14) uk0 = 0, ukM = 0, 0 ≤ k ≤ N, (3.15) vk0 = 0, vkM = 0, 0 ≤ k ≤ N. (3.16) 3.2. Conservation law. Theorem 3.1. Let {uki , vki : 0 ≤ i ≤M, 0 ≤ k ≤ N} be the solutions of (3.12)–(3.16). Denote Ek = ∥uk∥2 + ∥vk∥2 + 2τ k−1∑ l=0 |ul+ 1 2 |21, 0 ≤ k ≤ N. Then we have Ek = E0, 1 ≤ k ≤ N. Proof. Take the inner product of (3.12) with uk+ 1 2 , (δtu k+ 1 2 , uk+ 1 2 ) + (δtδ 2 xv k+ 1 2 , uk+ 1 2 )− (vk+ 1 2 , uk+ 1 2 ) + (∆xu k+ 1 2 , uk+ 1 2 ) + 1 3 (ψ(uk+ 1 2 , uk+ 1 2 ), uk+ 1 2 ) = 0, 0 ≤ k ≤ N − 1. From Lemma 2.2 it follows that 1 2τ (∥uk+1∥2 − ∥uk∥2) + 1 2τ (∥vk+1∥2 − ∥vk∥2) + |uk+ 1 2 |21 = 0. This equation can be written as ∥uk+1∥2 + ∥vk+1∥2 + 2τ |uk+ 1 2 |21 = ∥uk∥2 + ∥vk∥2. EJDE-2024/38 A DIFFERENCE SCHEME FOR ROSENAU-BURGERS EQUATION 5 Therefore, replacing the superscript k with l and summing for l from 0 to k − 1 yields Ek = ∥uk∥2 + ∥vk∥2 + 2τ k−1∑ l=0 |ul+ 1 2 |21 = Ek−1 = · · · = E0. □ 4. Solvability In this section, we analyze the unique solvability of the difference scheme estab- lished in (3.12)-(3.16). Theorem 4.1 (Browder theorem [16]). Let (H, (·, ·)) be a finite dimensional inner product space, ∥ · ∥ be the associated norm, and Π : H → H be continuous operator, ∃α > 0, ∀z ∈ H, ∥z∥ = α, Re(Π(z), z) ≥ 0. Then there exists a z∗ ∈ H satisfying ∥z∗∥ ≤ α such that Π(z∗) = 0. Theorem 4.2. The difference scheme (3.12)-(3.16) has at least one solution. Proof. Let uk = (uk0 , u k 1 , . . . , u k M ), vk = (vk0 , v k 1 , . . . , v k M ). It is easy to obtain u0 from (3.13) and (3.14). From (3.13)-(3.16), v0 can be found by computing an associated system of linear equations. Suppose that {uk, vk} have been determined, then we may regard {uk+ 1 2 , vk+ 1 2 } as unknowns and uk+1 i = 2u k+ 1 2 i − uki , vk+1 i = 2v k+ 1 2 i − vki , 0 ≤ i ≤M. We denote ωi = u k+ 1 2 i , zi = v k+ 1 2 i , 0 ≤ i ≤M, Then uk+1 i = 2wi − uki , vk+1 i = 2zi − vki , 0 ≤ i ≤M. From (3.12), (3.13), (3.15) and (3.16), the system of equations can be considered with respect to {wi}Mi=0 and {zi}Mi=0: 2 τ (ωi − uki ) + 2 τ (δ2xzi − δ2xv k i )− zi +∆xωi + ψ(ω, ω)i = 0, 1 ≤ i ≤M − 1, (4.1) zi = δ2xωi, 1 ≤ i ≤M − 1, (4.2) ω0 = 0, ωM = 0, (4.3) z0 = 0, zM = 0. (4.4) We define Π(ω) : V̊h → V̊h by Π(ω)i = { 2 τ (ωi − uki ) + 2 τ (δ 2 xzi − δ2xv k i )− zi +∆xωi + ψ(ω, ω)i, 1 ≤ i ≤M − 1, 0, i = 0,M. where (v0, v1, . . . , vM ) is determined by (3.13) and (3.15). Then Π(ω) is a contin- uous function in V̊h. Taking the inner product of Π(ω) with ω, using Lemma 2.1 yields (Π(ω), ω) = 2 τ [∥ω∥2 − (uk, ω)] + 2 τ [∥z∥2 − (δ2xu k, δ2xω)] + |ω|21 ≥ 2 τ [(∥ω∥2 − ∥uk∥∥ω∥) + (∥z∥2 − ∥vk∥∥z∥)] 6 S. DONG, X. ZHANG, Y. JIN EJDE-2024/38 ≥ 2 τ [(∥ω∥2 − ∥uk∥∥ω∥) + ( ∥z∥2 − ∥vk∥ · 6 L2 ∥ω∥ ) ] = 2 τ (∥ω∥ − ∥uk∥ − 6 L2 ∥vk∥)∥ω∥. Thus, when ∥ω∥ = ∥uk∥+ 6 L2 ∥vk∥, (Π(ω), ω) ≥ 0. By Theorem 4.1, there exists an ω∗ ∈ V̇h satisfying ∥ω∥ ≤ ∥uk∥+ 6 L2 ∥vk∥ such that (Π(ω∗)) = 0. Consequently, the difference scheme (3.12), (3.13), (3.15) and (3.16) has at least one solution uk+1 = 2ω∗ − uk. Observing (4.2) and (4.4), when (ω∗ 1 , ω ∗ 2 , . . . , ω ∗ M−1) is known, (z ∗ 1 , z ∗ 2 , . . . , z ∗ M−1) can be determined by (4.2) and (4.4) uniquely. Thus vk+1 i = 2zi − vki , 1 ≤ i ≤M − 1 . □ Theorem 4.3. When τ < 4/c43, the solution of the difference scheme (3.12)–(3.16) is unique. Proof. Suppose that both {u(1), v(1) ∈ V̊h} and {u(2), v(2) ∈ V̊h} are two solutions of (4.1)-(4.4). Then 2 τ (u (1) i − uki ) + 2 τ (δ2xv (1) i − δ2xv k i )− v (1) i +∆xu (1) i + ψ(u(1), u(1))i = 0, 1 ≤ i ≤M − 1, (4.5) v (1) i = δ2xu (1) i , 1 ≤ i ≤M − 1, (4.6) u (1) 0 = 0, u (1) M = 0, (4.7) v (1) 0 = 0, v (1) M = 0. (4.8) and 2 τ (u (2) i − uki ) + 2 τ (δ2xv (2) i − δ2xv k i )− v (2) i +∆xu (2) i + ψ(u(2), u(2))i = 0, 1 ≤ i ≤M − 1, (4.9) v (2) i = δ2xu (2) i , 1 ≤ i ≤M − 1, (4.10) u (2) 0 = 0, u (2) M = 0, (4.11) v (2) 0 = 0, v (2) M = 0. (4.12) Let ui = u (1) i − u (2) i , vi = v (1) i − v (2) i , 0 ≤ i ≤M. Subtracting (4.9)-(4.12) from (4.5)–(4.8) leads to 2 τ ui + 2 τ δ2xvi − vi +∆xui + [ψ(u(1), u(1))i − ψ(u(2), u(2))i] = 0, 1 ≤ i ≤M − 1, (4.13) vi = δ2xui, 1 ≤ i ≤M − 1, (4.14) u0 = 0, uM = 0, (4.15) v0 = 0, vM = 0. (4.16) Taking the inner product of (4.13) with u yields 2 τ ∥u∥2 + 2 τ (δ2xv, u)− (v, u) + (∆xu, u) = −(ψ(u(1), u(1))− ψ(u(2), u(2)), u) (4.17) EJDE-2024/38 A DIFFERENCE SCHEME FOR ROSENAU-BURGERS EQUATION 7 In view of the definition of u and Lemma 2.2, we have −(ψ(u(1), u(1))− ψ(u(2), u(2)), u) = −(ψ(u, u(1)), u) = −h 3 M−1∑ i=1 [ui∆xu (1) i +∆x(uu (1))i]ui = h 3 M−1∑ i=1 [u (1) i ∆x(u 2)i + (uu(1))i∆xui] ≤ 1 3 ( 2∥u∥∞∥u(1)∥ |u|1 + ∥u∥∞∥u(1)∥ |u|1 ) ≤ c3∥u∥∞|u|1 . Then it follows from (4.17) that 2 τ ∥u∥2 + 2 τ ∥v∥2 + |u|21 ≤ c3∥u∥∞|u|1. Using Lemma 2.1 gives 2 τ ∥u∥2 + |u|21 ≤ c3 ( ε|u|1 + 1 2ε ∥u∥ ) |u|1 ≤ c3ε|u|21 + c3ε|u|21 + 1 4c3ε ( c3 2ε )2∥u∥2 = 2c3ε|u|21 + c3 16ε3 ∥u∥ . Let ε = 1 2c3 . Then 2 τ ∥u∥ 2 ≤ c3 4 2 ∥u∥2. When τ < 4 c34 , we obtain ∥u∥ = 0. □ 5. Convergence In this section, we analyze the convergence of the difference scheme (3.12)-(3.16). Let c0 = max (x,t)∈[0,L]×[0,T ] {|u(x, t)|, |ux(x, t)|}. The convergent result is summarized as follows. Theorem 5.1. Let {u(x, t), v(x, t)} be the solutions of (3.1)-(3.5) and {uki , vki : 0 ≤ i ≤ M, 0 ≤ k ≤ N} be the solutions of the difference scheme (3.12)-(3.16). Also let eki = Uk i − uki , fki = V k i − vki , 0 ≤ i ≤M, 0 ≤ k ≤ N, and c4 = 3c0 2 + c0 2L2 2 + 3L 4 , c5 = e 3 2MT √ 6τM1, M = (c4 + 1), M1 = c2 2 + c1 2. If τ and h satisfy τ2 + h2 ≤ 1/c5 and 2c4τ ≤ 1/3, then the error estimate is |ek|1 ≤ c5(τ 2 + h2), 0 ≤ k ≤ N. 8 S. DONG, X. ZHANG, Y. JIN EJDE-2024/38 Proof. Subtracting (3.12)-(3.16) from (3.8), (3.9) and (3.11), a system of error equations is δte k+ 1 2 i + δtδ 2 xf k+ 1 2 i − f k+ 1 2 i +∆xe k+ 1 2 i + [ψ(Uk+ 1 2 , Uk+ 1 2 )i − ψ(uk+ 1 2 , uk+ 1 2 )i] = R k+ 1 2 i , 1 ≤ i ≤M − 1, 0 ≤ k ≤ N − 1, (5.1) fki = δ2xe k i +Qk i , 1 ≤ i ≤M − 1, 0 ≤ k ≤ N, (5.2) e0i = 0, 1 ≤ i ≤M − 1, (5.3) ek0 = 0, ekM = 0, 0 ≤ k ≤ N, (5.4) fk0 = 0, fkM = 0, 0 ≤ k ≤ N. (5.5) It follows from (5.2) that f k+ 1 2 i = δ2xe k+ 1 2 i +Q k+ 1 2 i , 1 ≤ i ≤M − 1, 0 ≤ k ≤ N − 1. Taking the inner product of (5.1) with δte k+ 1 2 i yields ∥δtek+ 1 2 ∥2 + (δtδ 2 xf k+ 1 2 , δte k+ 1 2 )− (fk+ 1 2 , δte k+ 1 2 ) + (∆xe k+ 1 2 , δte k+ 1 2 ) + (ψ(Uk+ 1 2 , Uk+ 1 2 )− ψ(uk+ 1 2 , uk+ 1 2 ), δte k+ 1 2 ) = (Rk+ 1 2 , δte k+ 1 2 ), for 1 ≤ k ≤ N − 1. From Lemma 2.1, it follows that −(δtδ 2 xf k+ 1 2 , δte k+ 1 2 ) = −(δtf k+ 1 2 , δtδ 2 xe k+ 1 2 ) = −(δtf k+ 1 2 , δt(f k+ 1 2 −Qk+ 1 2 )) = −(δtf k+ 1 2 , δtf k+ 1 2 ) + (δtf k+ 1 2 , δtQ k+ 1 2 ) ≤ −∥δtfk+ 1 2 ∥2 + ∥δtfk+ 1 2 ∥ t∥δtQk+ 1 2 ∥, (fk+ 1 2 , δte k+ 1 2 ) = (δ2xe k+ 1 2 +Qk+ 1 2 , δte k+ 1 2 ) ≤ − 1 2τ (|ek+1|21 − |ek|21) + ∥Qk+ 1 2 ∥ ∥δtek+ 1 2 ∥, and −(∆xe k+ 1 2 , δte k+ 1 2 ) ≤ ∥∆xe k+ 1 2 ∥ ∥δtek+ 1 2 ∥, From the definition of ψ(u, v)i and applying Lemma 2.2, we obtain − (ψ(Uk+ 1 2 , Uk+ 1 2 )− ψ(uk+ 1 2 , uk+ 1 2 ), δte k+ 1 2 ) = −(ψ(Uk+ 1 2 , ek+ 1 2 ) + ψ(ek+ 1 2 , Uk+ 1 2 )− ψ(ek+ 1 2 , ek+ 1 2 ), δte k+ 1 2 ). Note that (ψ(ek+ 1 2 , ek+ 1 2 ), δte k+ 1 2 ) = (ψ(ek+ 1 2 , ek + τ 2 δte k+ 1 2 ), δte k+ 1 2 ) = (ψ(ek+ 1 2 , ek), δte k+ 1 2 ) + τ 2 (ψ(ek+ 1 2 , δte k+ 1 2 ), δte k+ 1 2 ) = (ψ(ek+ 1 2 , ek), δte k+ 1 2 ). Thus we obtain − (ψ(Uk+ 1 2 , Uk+ 1 2 )− ψ(uk+ 1 2 , uk+ 1 2 ), δte k+ 1 2 ) = −(ψ(Uk+ 1 2 , ek+ 1 2 ) + ψ(ek+ 1 2 , Uk+ 1 2 )− ψ(ek+ 1 2 , ek), δte k+ 1 2 ) EJDE-2024/38 A DIFFERENCE SCHEME FOR ROSENAU-BURGERS EQUATION 9 = −h 3 M−1∑ i=1 [U k+ 1 2 i ∆xe k+ 1 2 i + 2∆x(U k+ 1 2 ek+ 1 2 )i + e k+ 1 2 i ∆xU k+ 1 2 i ]δte k+ 1 2 i + h 3 M−1∑ i=1 [e k+ 1 2 i ∆xe k i +∆x(e k+ 1 2 ek)i]δte k+ 1 2 i = −h 3 M−1∑ i=1 (3U k+ 1 2 i ∆xe k+ 1 2 i + e k+ 1 2 i+1 δxU k+ 1 2 i+ 1 2 + e k+ 1 2 i−1 δxU k+ 1 2 i− 1 2 + e k+ 1 2 i ∆xU k+ 1 2 i )δte k+ 1 2 i + h 3 M−1∑ i=1 (2e k+ 1 2 i ∆xe k i + 1 2 eki+1δxe k+ 1 2 i+ 1 2 + 1 2 eki−1δxe k+ 1 2 i− 1 2 )δte k+ 1 2 i ≤ c0|ek+ 1 2 |1 · ∥δtek+ 1 2 ∥+ c0∥ek+ 1 2 ∥ · ∥δtek+ 1 2 ∥ + 1 3 (2∥ek+ 1 2 ∥∞ · |ek|1 + ∥ek∥∞ · |ek+ 1 2 |1)∥δtek+ 1 2 ∥ ≤ c0|ek+ 1 2 |1 · ∥δtek+ 1 2 ∥+ c0∥ek+ 1 2 ∥ · ∥δtek+ 1 2 ∥+ √ L 2 |ek+ 1 2 |1 · ∥δtek+ 1 2 ∥ ≤ ε1∥δtek+ 1 2 ∥2 + c0 2 4ε1 |ek+ 1 2 |21 + ε2∥δtek+ 1 2 ∥2 + c0 2 4ε2 ∥ek+ 1 2 ∥21 + ε3∥δtek+ 1 2 ∥2 + 1 4ε3 L 4 |ek+ 1 2 |21 ≤ (ε1 + ε2 + ε2)∥δtek+ 1 2 ∥2 + ( c0 2 4ε1 + c0 2 4ε2 L2 6 + L 16ε3 )|ek+ 1 2 |21. Let ε1 = ε2 = ε3 = 1 12 . Then −(ψ(Uk+ 1 2 , Uk+ 1 2 )− ψ(uk+ 1 2 , uk+ 1 2 ), δte k+ 1 2 ) ≤ 1 4 ∥δtek+ 1 2 ∥2 + c4|ek+ 1 2 |21. Substituting above equations into equation (5.1) gives ∥δtek+ 1 2 ∥2 ≤ −∥δtfk+ 1 2 ∥2 + ∥δtfk+ 1 2 ∥ ∥δtQk+ 1 2 ∥ − 1 2τ (|ek+1|21 − |ek|21) + ∥Qk+ 1 2 ∥ · ∥δtek+ 1 2 ∥+ ∥∆xe k+ 1 2 ∥ · ∥δtek+ 1 2 ∥+ 1 4 ∥δtek+ 1 2 ∥2 + c4|ek+ 1 2 |21 ≤ 1 4 ∥δtQk+ 1 2 ∥ − 1 2τ (|ek+1|21 − |ek|21) + ∥Qk+ 1 2 ∥2 + 1 4 ∥δtek+ 1 2 ∥2 + |ek+ 1 2 |21 + 1 4 ∥δtek+ 1 2 ∥2 + 1 4 ∥δtek+ 1 2 ∥2 + c4|k+ 1 2 |21 + ∥Rk+ 1 2 ∥2 + 1 4 ∥δtek+ 1 2 ∥2. (5.6) From (3.10), simplifying and rearranging (5.6) leads to |ek+1|12 ≤ |ek|12 + 2τ c22 4 (τ2 + h2)2 + 2τc22(h 2)2 + 2τc1 2(τ2 + h2)2 + τ(c4 + 1)|ek+1|21 + τ(c4 + 1)|ek|21. Then (1− τM)|ek+1|12 ≤ (1 + τM)|ek|12 + 2τM1(τ 2 + h2)2, 0 ≤ k ≤ N − 1. If τM ≤ 1 3 , then |ek+1|12 ≤ (1 + 3τM)|ek|12 + 6τM1(τ 2 + h2)2, 0 ≤ k ≤ N − 1. 10 S. DONG, X. ZHANG, Y. JIN EJDE-2024/38 Using Gronwall’s inequality we obtain |ek|21 ≤ e3Mkτ6τM1(τ 2 + h2)2 ≤ e3MT 6τM1(τ 2 + h2)2, 0 ≤ k ≤ N. □ From Theorem 5.1 and Lemma 2.1, we find that ∥ek∥∞ ≤ √ L 2 |ek|1 ≤ c5 √ L 2 (τ2 + h2), 0 ≤ k ≤ N. To demonstrate the results in the previous sections and confirm the accuracy of our method, we consider the Rosenau-Burgers equation with the following initial- boundary value problem. ut + uxxxxt − uxx + ux + uux = 0, x ∈ [0, 1], t ∈ [0, 1], (5.7) u(x, 0) = u0(x) = x4(1− x)4, x ∈ [0, 1], (5.8) u(0, t) = u(1, t) = 0, uxx(0, t) = uxx(1, t) = 0. (5.9) Since we do not know the exact solution of (5.7)-(5.9), to obtain the error esti- mate, we consider the solution on mesh h = 1/256 as the reference solution, which is fine enough as a referenced exact solution for obtaining the error estimation. When the exact solution is known, we define the discrete error in the L∞-norm as follows E∞(h, τ) = max 1≤i≤M,0≤k≤N |Uk i − uki |, where Uk i and uki represent the exact solution and the numerical solution, respec- tively. Furthermore, denote the spatial and temporal convergence orders, respec- tively, as Orderh∞ = log2 E∞(2h, τ) E∞(h, τ) , Orderτ∞ = log2 E∞(h, 2τ) E∞(h, τ) . Figure 1 shows the three dimensional image of numerical solutions. From Figure 2, we can know that with the time going by, the waveform changes and the peak value decreases. It shows that our scheme is stable. Table 1 shows that the numerical results are conservative at different t where Ek is defined in Theorem 3.1. Table 2 and Table 3 list the errors and corresponding convergence orders. It shows that the maximal errors reduce with the decrease of the spatial step h and time step τ . The convergence orders are both two in space and time in L∞-norm, which are consistent with our theoretical results. It reveals that the numerical method in this paper is accurate and efficient. Table 1. Discrete energy Ek at h=1/256 and τ = 0.01. t Ek t=0.1 0.004792856601 t=0.3 0.004792856601 t=0.5 0.004792856601 t=0.7 0.004792856601 t=0.9 0.004792856601 Acknowledgments. This work was supported by the Natural Science Foundation of Jilin Province (No. YDZJ202101ZYTS136). EJDE-2024/38 A DIFFERENCE SCHEME FOR ROSENAU-BURGERS EQUATION 11 Figure 1. Three dimensional image of numerical solutions at h=1/256 and τ=0.1. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 10 -3 t=0 t=0.5 t=1 Figure 2. Numerical solutions with h=0.01 and τ=0.1 at various times. Table 2. Errors and temporal convergence orders when t = 1.0. h τ E∞(h, τ) Orderτ∞ h=1/128 τ = 1/8 3.3233e− 09 – h=1/128 τ = 1/16 8.2855e− 10 2.0040 h=1/128 τ = 1/32 2.0475e− 10 2.0168 h=1/128 τ = 1/64 4.9024e− 11 2.0623 References [1] D. J. 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Sitong Dong Department of Mathematics, Yanbian University, Yanji 133002, China Email address: 394018165@qq.com Xin Zhang Department of Mathematics Science, Harbin Engineering University, Harbin 150000, China Email address: zhangxin2022@hrbeu.edu.cn Yuanfeng Jin Department of Mathematics, Yanbian University, Yanji 133002, China Email address: yfkim@ybu.edu.cn 1. Introduction 2. Preliminaries 3. Nnonlinear conservative difference scheme 3.1. Construction of difference scheme 3.2. Conservation law 4. Solvability 5. Convergence Acknowledgments References