Quartic B splines collocation method for numerical solution of the MRLW equation
In this paper, numerical solutions of the modified regularized long wave (MRLW)
equation are obtained by a method based on collocation of quartic B splines. Applying the
von-Neumann stability analysis, the proposed method is shown to be unconditionally
stable. The method is applied on some test examples, and the numerical results have been
compared with the exact solutions. The and in the solutions show the efficiency of
the method computationally.
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e test examples, and the numerical results have been compared with the exact solutions. The and in the solutions show the efficiency of the method computationally. Keywords: MRLW equation; quartic B spline; collocation method; finite difference. Email: nvdungkiev@yahoo.com Received 02 December 2017 Accepted for publication 25 December 2017 1. INTRODUCTION In this work, we consider the solution of the mGRLW equation u + αu + εu u − βu = 0, (1) x ∈ [a, b], t ∈ [0, T], with the initial condition u(x, 0) = f(x), x ∈ [a, b], (2) and the boundary condition u(a, t) = 0, u(b, t) = 0 u (a, t) = u (a, t) = 0 (3) u (a, t) = u (b, t) = 0, where α, ε, β are constants, β > 0. 6 TRƯỜNG ĐẠI HỌC THỦ ĐÔ HÀ NỘI The MRLW equations play a dominant role in many branches of science and engineering [1]. In the past several years, many different methods have been used to estimate the solution of the MRLW equation, for example, see [1, 3]. In this present work, we have applied the quartic B spline collocation method to the MRLW equations. This work is built as follow: in Section 2, numerical scheme is presented. Section 3, is devoted to stability analysis of the method. The numerical results are discussed in Section 4. A conclusion is given at the end of the paper in Section 5. 2. QUINTIC B – SPLINE COLLOCATION METHOD The interval [ , ] is partitioned in to a mesh of uniform lengthh = x − x by the knots x , i = 0 , N such that a = x < x < ⋯ < x < x = b. Our numerical treatment for the MRLW equation using the collocation method with quartic B spline is to find an approximate solution U(x,t) to the exact solution u(x,t) in the form U(x, t) = ∑ δ (t)B (x), (4) where δ (t) are time-dependent quantities to be determined from the boundary conditions and collocation form of the differential equations. Also B (x) are the quartic B spline basis functions at knots, given by [4]. (x − x ) , x ≤ x ≤ x ⎧ ⎪(x − x ) − 5(x − x ) , ⎪ x ≤ x ≤ x ⎪ ⎪(x − x ) − 5(x − x ) + 10(x − x ) , x ≤ x ≤ x 1 ( ) B x = h ⎨(x − x) − 5(x − x) , x ≤ x ≤ x ⎪ ⎪ ⎪ (x − x) , x ≤ x ≤ x ⎪ ⎩0, x x . The value of B (x) and its derivatives may be tabulated as in Table 1. U = δ + 11δ + 11δ + δ 4 U′ = (−δ − 3δ + 3δ + δ ) h 12 U′′ = (δ − δ − δ + δ ). h TẠP CHÍ KHOA HỌC SỐ 20/2017 7 Table 1. , ′ , and ′′ at the node points x B (x) 0 1 11 11 1 0 4 12 12 4 B′ (x) 0 − − 0 h h h h 12 12 12 12 B′′ (x) 0 − − 0 h h h h Using the finite difference method, from the equation (1), we have: ( ) ( ) ( ) ( ) + ε(u) (u ) + α = 0. (5) Using the value given in Table 1, Eq. (5) can be calculated at the knots x , i = 0 , N so that Eq. (5) reduces to: a δ + a δ + a δ + a δ = b δ + b δ + b δ + b δ , (6) where a = 2h − 4hα∆t − 24β − 4p + 4q, a = 22h − 12hα∆t + 24β − 12p + 22q, a = 22h + 12hα∆t + 24β + 12p + 22q, a = 2h + 4hα∆t − 24β + 4p + 4q , b = 2h + 4hα∆t − 24β − 4p , b = 22h + 12hα∆t − 24β − 12p , b = 22h − 12hα∆t + 24β + 12p , b = 2h − 4hα∆t − 24β + 4p , p = h∆tεL , q = h ε∆tL L , L = δ + 11δ + 11δ + δ , 4 L = (−δ − 3δ + 3δ + δ ). h 8 TRƯỜNG ĐẠI HỌC THỦ ĐÔ HÀ NỘI The system (6) consists of N + 1 equations in the N + 4 knowns (δ , δ , , δ ) . To get a solution to this system, we need four additional constraints. These constraints are obtained from the boundary conditions (3) and can be used to eliminate from the system (6). Then, we get the matrix system equation A(δ )δ = B(δ )δ + r, (7) Where the matrix A(δ ), B(δ ) are penta-diagonal (N + 1) × (N + 1) matrices and r is the N + 1 dimensional colum vector. The algorithm is then used to solve the system (7). We apply the initial condition U(x, 0) = ∑ δ B (x), (8) then we need that the approximately solution is satisfied following conditions U(x , 0) = f(x ) ⎧ U (x , 0) = U (a, 0) = 0 ⎪ U (x , 0) = U (b, 0) = 0 (9) ⎨U (x , 0) = U (a, 0) = 0 ⎪U (x , 0) = U (b, 0) = 0 ⎩ i = 0,1, , N. Eliminating δ , δ and δ from the system (9), we get Aδ = r, where A is the quartic-diagonal matrix given by: 3 1 0 ... ... 0 37 43 1 0 ... ... 0 4 4 1 11 11 1 0 ... ... 0 A ... ... ... ... ... ... ... 0 ... 0 1 11 11 1 0 ... 0 1 1 and δ = (δ , δ , , δ ) , r = (f(x ), f(x ), , f(x )) . 3. STABILITY ANALYSIS In this section, we present the stability of the quartic B spline approximation (6) using the von-Neumann method. According to the von-Neumann method, we have: δ = ξ exp(iγmh) , i = √−1, (10) where γ is the mode number and h is the element size. TẠP CHÍ KHOA HỌC SỐ 20/2017 9 Being applicable to only linear schemes the nonlinear term U U is linearized by taking U as a locally constant value θ. The linearized form of proposed scheme is given as σ δ + σ δ + σ δ + σ δ = σ δ + σ δ + σ δ + σ δ (11) where 4a 12β 12a 12β σ = 1 − − , σ = 11 − + , h h h h 12a 12β 4a 12β σ = 11 + + , σ = 1 + − , h h h h (α + εθ )∆t = . h Substitretion of δ = exp(iγjh)ξ ,into Eq. (11) leads to ξ[σ exp(−2ihγ) + σ exp(−iγh) + σ + σ exp(iγh)] = σ exp(−2iγh) + σ exp(−iγh) + σ + σ exp(iγh). (12) Simplifying Eq. (12), we get: A − iB = , C + iB It is clear that C + B = A + B . So | | = 1. Therefore, the linearized numerical scheme for the MRLW equation is unconditionally stable. 4. NUMERICAL EXAMPLE We now obtain the numerical solution of the MRLW equation for some problems. To show the efficiency of the present method for our problem in comparison with the exact solution, we report L and L using formula: L = max |U(x , t) − u(x , t)|, L = h |U(x , t) − u(x , t)| , where U is numerical solution and u denotes exact solution. Three invariants of motion which correspond to the conservation of mass, momentum, and energy are given as: 10 TRƯỜNG ĐẠI HỌC THỦ ĐÔ HÀ NỘI I = udx, I = (u + βu )dx, I 2β(p + 1) = u − u dx. ε We have the exact solution of the MRLW is: A u(x, t) = , cosh (ρ(x − x − ct)) ( )( )( ) where = , = . The initial condition of Equation (1) given by: A f(x) = . cosh (ρ(x − x )) We take α = 1.1, ε = 64, β = 2, a = 0, b = 100, x = 30, ∆t = 0.025 and ∆t = 0.01, h = 0.1 and h = 0.2, t ∈ [0, 20]. The values of the variants and the error norms at several times are listed in Table 2 and Table 3. From Table 2, we see that, changes of variants I , I × 10 and I × 10 from their initial value are less than 0.1, 0.2 and 0.9, respectively. The error nomrs L , L are less than 0.009695 and 0.008033, respectively. In Table 3, changes of variants I , I × 10 and I × 10 from their initial value are less than 0.7, 0.4 and 0.6, respectively. The error nomrs L , L are less than 0.007553 and 0.008033, respectively. Table 2. Variants and error norms of the MRLW equation with = 1.1, = 1.11 = 64, = 2, = 0, = 100, = 30, ∆ = 0.01, ℎ = 0.1, ∈ [0, 20] t 0 5 10 15 20 I 1.251299 1.287541 1.315251 1.335511 1.347595 I 0.037046 0.036778 0.036835 0.036867 0.036847 I -0.001087 -0.001035 -0.001022 -0.001013 -0.001004 L 0.007105 0.006936 0.007444 0.008531 0.009695 L 0.008033 0.005587 0.003866 0.002957 0.002993 Figure 1 shows approximate solution graphs at t = 0, 5, 10, 15, 20. TẠP CHÍ KHOA HỌC SỐ 20/2017 11 Figure 1. Single solitary wave with = 1.1, = 1.11, = 64, = 2, = 0, = 100, = 30, ∆ = 0.01, ℎ = 0.2, = 0, 5,10, 15, 20. Table 3. Variants and error norms of the MRLW equation with = 1.1, = 1.11 = 64, = 2, = 0, = 100, = 30, ∆ = 0.01, ℎ = 0.2, ∈ [0, 20] t 0 5 10 15 20 I 1.250960 1.283776 1.304115 1.313904 1.314098 I 0.031271 0.030893 0.030752 0.030577 0.030395 I -0.000546 -0.000488 -0.000464 -0.000443 -0.000426 L 0.007553 0.007163 0.006965 0.006883 0.006890 L 0.008033 0.005587 0.003866 0.002670 0.002472 The plot of the estimated solution at time t = 0, 5, 10, 15, 20 in Figure 2. Figure 2. Single solitary wave with = 1.1, = 1.11, = 64, = 2, = 0, = 100, = 30, ∆ = 0.01, ℎ = 0.2, = 0, 5,10, 15, 20. 12 TRƯỜNG ĐẠI HỌC THỦ ĐÔ HÀ NỘI To get more the variants and error norms, we choose two sets of parameters by taking different values of h = 0.1 and h = 0.2 and the same values of = 1.1, = 1.11, ε = 128, β = 2, a = 0, b = 100, x = 30, ∆t = 0.01. The variants and error norms are calculated from time t = 0 to t = 20. The numerical results are given Table 4 and Table 5. From Table 4, we see that, changes of variants I × 10, I × 10 and I × 10 from their initial value are less than 0.7, 0.1 and 0.3, respectively. The error nomrs L , L are less than 0.006855 and 0.005681, respectively. In Table 5, changes of variants I × 10, I × 10 and I × 10 from their initial value are less than 0.4, 0.6 and 0.4, respectively. The error nomrs L , L are less than 0.005341 and 0.005680, respectively. Error graphs are shown in Figure 3 and Figure 4 at t = 0, 5, 10, 15 and t = 20. Table 4. Variants and error norms of the MRLW equation with = 1.1, = 1.11 = 128, = 2, = 0, = 100, = 30, ∆ = 0.01, ℎ = 0.1, ∈ [0, 20] t 0 5 10 15 20 I 0.884802 0.910429 0.930023 0.944348 0.952893 I 0.018523 0.018389 0.018418 0.018433 0.018424 I -0.000272 -0.000259 -0.000256 -0.000253 -0.000251 L 0.005024 0.004905 0.005264 0.006033 0.006855 L 0.005681 0.003950 0.002734 0.002091 0.002117 Table 5. Variants and error norms of the MRLW equation with = 1.1, = 1.11 = 128, = 2, = 0, = 100, = 30, ∆ = 0.01, ℎ = 0.2, ∈ [0, 20] t 0 5 10 15 20 I 0.884562 0.907767 0.922149 0.929070 0.929208 I 0.015636 0.015447 0.015376 0.015289 0.015120 I -0.000137 -0.000122 -0.000116 -0.000111 -0.000106 L 0.005341 0.005065 0.004925 0.004867 0.004872 L 0.005680 0.003950 0.002734 0.001888 0.001748 TẠP CHÍ KHOA HỌC SỐ 20/2017 13 a) h = 0.1 b) h= 0.2 Figure 3. Single solitary wave with = 1.1, = 1.11, = 128, = 2, = 0, = 100, = 30, ∆ = 0.01, ℎ = 0.1, ℎ = 0.2, = 0, 5,10, 15, 20. Finally, we choose the parameter sets α = 1.5, ε = 256, β = 2, a = 0, b = 100, x = 30, ∆t = 0.01, c = 1.31, h = 0.1and h = 0.2, t ∈ [0, 20]. The obtained results are given in Table 6 and Table 7. From Table 6, we see that, changes of variants I × 10, I × 10 and I × 10 from their initial value are less than 0.4, 0.2 and 0.7, respectively. The error nomrs L , L are less than 0.004010 and 0.004683, respectively. In Table 7, changes of variants I × 10, I × 10 and I × 10 from their initial value are less than 0.3, 0.5 and 0.2, respectively. Besides, we observed that the error in the L , L norm in those tables is small. Table 6. Variants and error norms of the MRLW equation with = 1.3, = 1.31 = 256, = 2, = 0, = 100, = 30, ∆ = 0.01, ℎ = 0.1, ∈ [0, 10] t 0 2 4 6 8 10 I 0.666901 0.677352 0.686507 0.694563 0.701611 0.707678 I 0.010805 0.010699 0.010714 0.010721 0.010730 0.010738 I -0.000092 -0.000086 -0.000088 -0.000087 -0.000087 -0.000087 L 0.003753 0.003671 0.003636 0.003676 0.003804 0.004010 L 0.004683 0.004010 0.003427 0.002925 0.002494 0.002126 14 TRƯỜNG ĐẠI HỌC THỦ ĐÔ HÀ NỘI Table 7. Variants and error norms of the MRLW equation with = 1.3, = 1.31 = 256, = 2, = 0, = 100, = 30, ∆ = 0.01, ℎ = 0.2, ∈ [0, 10] t 0 2 4 6 8 10 I 0.666670 0.676480 0.684479 0.690849 0.695687 0.699124 I 0.008842 0.008723 0.008715 0.008698 0.008674 0.008648 I -0.000046 -0.000042 -0.000042 -0.000041 -0.000040 -0.000039 L 0.004040 0.003923 0.003836 0.003773 0.003732 0.003708 L 0.004683 0.004010 0.003427 0.002925 0.002494 0.002126 5. CONCLUSION In this work, we have used the quartic B spline collocation method for solution of the MRLW equation. The stability analysis of the method is shown to be unconditionally stable. The numerical results given in the previous section demonstrate the good accuracy and stability of the proposed scheme in this research. REFERENCES 1. A.Gul Kaplan and Y.Maz Derel (2017), “Numerical solutions of the MRLW equation using moving least square collocation method”, Commun.Fac.Sci.Univ.Ank.Series A1 Vol. 66(2), pp.349-361. 2. S.Islam, F.Haq and I.A.Tirmizi (2010), “Collocation method using quartic B-spline for numerical solution of the modified equal width wave equation”, J. Appl. Math. Inform., Vol. 28 (3-4), pp.611-624. 3. R.Mohammadi (2015),“Exponential B spline collocation method for numerical solution of the generalized regularized long wave equation”, Chin. Phys. B, Vol. 24(5), 050206, pp.1-14. 4. P.M.Prenter (1975), “Splines and Variational Methods”, Wiley, New York. 5. M.Zarebnia and R.Parvaz (2013), “Cubic B-spline collocation method for numerical solution of the Benjamin-Bona-Mahony-Burgers equation”, International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering, Vol. 7(3), pp.540-543. PHƯƠNG PHÁP KẾT NỐI TRƠN CÁC ĐA THỨC BẬC BỐN GIẢI PHƯƠNG TRÌNH MRLW Tóm tắt: Trong bài báo này, nghiệm số của phương trình sóng dài chính quy cải biên (MRLW) sẽ tìm được dựa trên cơ sở sử dụng sự kết nối trơn các đa thức bậc 4. Sử dụng phương pháp Von–Neumann hệ phương trình sai phân ổn định vô điều kiện. Phương pháp giải nêu ra được áp dụng cho một số ví dụ và so sánh với nghiệm chính xác. Kết quả tính toán cho thấy hiệu lực của phương pháp đề xuất. Từ khóa: Phương trình MRLW, spline bậc 4, phương pháp collocation, phương pháp sai phân hữu hạn.
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