J. Nig. Soc. Phys. Sci. 4 (2022) 797 Journal of the Nigerian Society of Physical Sciences A One-Step Block Hybrid Integrator for Solving Fifth Order Korteweg-de Vries Equations Olumide O. Olaiyaa, Mark I. Modebeia,b,∗, Saheed A. Belloc aMathematics Programme, National Mathematical Centre, Abuja, Nigeria bDepartment of Mathematics, University of Abuja, Nigeria cNational Water Resources Institute, Kaduna, Nigeria Abstract Fifth-order Korteweg-de Vries (KdV) equations, arise in modeling waves phenomena such as the propagation of shallow water waves over a flat surface, gravity-capillary waves and sound waves in plasmas. In this work, a one-step block hybrid linear multistep method was derived using the collocation technique, to solve fifth-order KdV models via the Method of Line (MoL). The consistency, stability and convergence of the method were established. The efficiency of the method can be seen from comparison of the exact solutions of problems and other methods cited from literature. DOI:10.46481/jnsps.2022.797 Keywords: Korteweg-de Vries (KdV) equations, Fifth-order PDE, Linear multistep, Block Method, Convergence Article History : Received: 03 May 2022 Received in revised form: 12 July 2022 Accepted for publication: 25 July 2022 Published: 19 August 2022 c© 2022 The Author(s). Published by the Nigerian Society of Physical Sciences under the terms of the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0). Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Communicated by: T. Latunde 1. Introduction In this work, the numerical solution of fifth order PDE of the form;{ a(x)ytt + b(x)yxxxxx = G(x, t, y, y2, yx, yt, yxx, yxxx), y(x, b) = g1(x), y(a, t) = g3(t) (1) defined on the domain Ω = {(x, t) : a < x < b, c < t < d}, and the boundary ∂Ω. where a, b, c, d are real numbers. Formulation of models into PDEs of the type in equation (1) arise in sciences, for example, fifth-order Korteweg-de Vries (KdV) type equations, models different wave phenomena which ∗Corresponding author tel. no: +2348031576262 Email address: gmarc.ify@gmail.com (Mark I. Modebei) includes the propagation of shallow water waves over a flat sur- face, gravity-capillary waves and sound wave propagation in plasmas see [1, 2, 3]. Prominent examples includes the ”good” Boussinesq equation, the Kaup-Kupershmidt equation and an extended KdV5 equation, [4]. These equations model phe- nomenon like laser optics, nonlinear dispersive waves in a wide range of applications, water waves, and plasma: generally, these are PDEs with higher order spatial derivatives, [4, 5, 6]. Some of the notable general (linear and nonlinear) fifth order KdV equations include though not limited to: the Kawahara equa- tion [4]; the Lax equation [7]; the Caudrey-Dodd-Gibbon (C-D- G) equation [8]; the fifth-order KdV equation [9]; the Sawada- Kotera (SK) equation [10]. They take the general form Ayt + By 2yx + Cyxyxx + Dyyxxx + Eyxxxxx = 0 (2) 1 Olaiya et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 797 2 with appropriate initial-boundary conditions, where A, B, C, D, E are constants. the form (2) is referred to as the generalized fifth- order Korteweg-de Vries (GFKdV), [11, 12]. These GFKdV equations models diverse important physi- cal phenomena. This equation do not just show the movement of long waves in shallow water under gravity and in a one- dimensional nonlinear lattice, but at the same time, it is a sig- nificant mathematical model for magneto-sound propagation in plasmas [13] and a chain of coupled nonlinear oscillators [14]. Obtaining the exact solution of the GFKdV equation ap- pears to be unreachable in most cases especially for the nonlin- ear case, save the special case of solitary waves in [15]. Some methods which are semi numerical and complete numerical in literature that were derived for solving fifth order KdV types in- clude, Modified Variational Iteration Technique [11], Modified Variational Iteration Algorithm-II (MVIA-II) [12], He’s Varia- tional Iteration Method, [16], homotopy analysis method, [17], Group analysis method [18], among others. In this work, we derive a 1-Step Block Hybrid Integrator (1SBHI), assembled in block form using collocation technique, for the solution of fifth-order Korteweg-de Vries (KdV) type equations using the MOLs approach, see [19, 20, 21]. The linear multistep method (LMM) derived using the collocation technique is conveniently used to approximate, with high ac- curacy, continuous Initial-Boundary Value Problems (IBVPs) of both the ordinary and partial differential equations [20]. It has several advantages among which are the fact that they do not require any staring value to kick-start their implementation, they are self-starting [22, 23]. They also have the advantage of producing smaller global errors (at the end of the range of integration) than those produced by the step-by-step methods due to the presence of accumulated errors at each step in the step-by-step method, see [24, 25, 26, 27, 28]. The Method of Lines (MOLs) approach is a very impor- tant tool used for solving Partial Differential Equations (PDEs), where a PDE is transformed into a system of Ordinary Differ- ential Equations (ODEs) whereby appropriate derivatives are replaced by finite difference approximations. In this work, we transform the PDEs into a system of ODEs such that only one of the spatial derivatives is substituted with central difference ap- proximations. The system that results is solved using 1SHBI. In the case of this work, we discretize the space variable t with meshing ∆t = d − c M , tm = c + m∆t, m = 0, 1, . . . M and then define the vector y = [y1,1, y1,2, y2,1, . . . , yn,m−1, yn−1,m, . . . , yn−1,m−1] T and G = [G1,1, G1,2, G2,1, . . . , Gn,m−1, Gn−1,m, . . . , Gn−1,m−1] T where ym ≈ y(x, tm). The central differences approximation for- mulae for the first and second derivatives are yt ≈ ym+1 − ym−1 (2∆t) ytt ≈ ym+1 − 2ym + ym−1 (∆t)2 The solution y(x, t), of equation (1), where (x, t) is in the rectan- gle [a, b]×[c, d], is obtained by solving the system of fifth-order ODEs in the spatial variable x. Here the mesh of x is spaced is: πN = a = x0 < x1 < .. . < xN−1 < xN = b, with the step-size h given as h = b − a N , xn = a + nh, n = 0, 1, . . . , N Then, the equation (1) has the semidiscretized form dy5n,m d x5 ≈− an,m bn,m + 1 bn,m ( ym+1 − 2ym + ym−1 (∆t)2 + Gn,m ) (3) where Gn,m = xn, tm, yn,m, y2n,m, dyn,md x , ym+1 − um−1(2∆t) , dy 2 n,m d x2 , dy3n,m d x3  and bn,m , 0 for n = 0, 1, . . . , N and m = 0, 1, . . . , M. The equivalent form for equation (3) is the following system of fifth order ODE given by y(5) = f (x, y, y′, y′′, y′′′, y(4)), a < x < b (4) subject to the boundary conditions: y(a) = y0, y’(a) = y ′ 0, y”(a) = y ′′ 0 , y(b) = y1n,m, y ′(b) = y2n,m where f (x, y, y′, y′′, y′′′, y(4)) = AY + g and A is a k by k matrix of constants with (k = (N − 1)(M − 1)) which results from the semi-discretized system of equation (3), expressed in the form the equation (4) and hence solved using 1SBHI. Here g is a vector of constants. Note that j in y jn,m, for j = 1, 2, are only index notation for different yn,m. In what follows, the derivation of the approximate solution of equation (4) is discussed. It is noteworthy to see that this technique is easy to de- rive and implement for solving this class of problem defined in equation (1). 2. Derivation of the Method Suppose the approximate solution yn(x) of equation (4) have the continuous form y(x) ≈ u(x) = 10∑ j=0 a j x j (5) where its fifth derivative is given by y(v)(x) ≈ u(v)(x) = 10∑ j=5 j( j−1)( j−2)( j−3)( j−4)a j x j−5(6) Evaluating equation (5) at the points x = xn+v j , j = 0(1)4 where v0 = 0, v1 = 1 6 , v2 = 1 3 , v3 = 2 3 , v4 = 5 6 and equation (6) at the 2 Olaiya et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 797 3 points x = xn+v j , j = 0(1)5 where v5 = 1, the following system of equations are obtained. u(xn) = yn; u ′(xn) = y ′ n; u ′′(xn) = y ′′ n ; u ′′′(xn) = y ′′′ n ; u(iv)(xn) = y (iv) n ; u (v)(xn) = fn; u (v)(xn+v) = fn+v j, j = 1(1)5. (7) Solving the above system simultaneously with the use of CAS in Mathematica 12.0, the coefficients a j, j = 0(1)10 are ob- tained (though not included here due to their cumbersome terms). They are in turn substituted into equation (5), to obtain the fol- lowing continuous method: yn+vk = 4∑ j=0 αkj h iy( j)n + h 5 5∑ j=0 βkj fn+v j ∣∣∣∣∣ k=1(1)5 (8) where α j and β j are shown in the Table 1. The first derivative of equation (8) is given as y′n+vk = 4∑ i=1 αih i−1y(i)n + h 4 5∑ j=0 βi fn+vi ∣∣∣∣∣ k=1(1)5 (9) here, α j and β j are shown in the Table 2. The second derivative of equation (8) is given as y′′n+vk = 4∑ i=2 αih i−2y(i)n + h 3 5∑ j=0 βi fn+vi ∣∣∣∣∣ k=1(1)5 (10) where α j and β j are shown in the Table 3 The third derivative of equation (8) is given as y′′′n+vk = 4∑ i=3 αih i−3y(i)n + h 2 5∑ j=0 βi fn+vi ∣∣∣∣∣ k=1(1)5 (11) here α j and β j are shown in the Table 4. The fourth derivative of equation (8) is given as y(iv)n+vk = y (iv) n + h 5∑ j=0 βi fn+vi ∣∣∣∣∣ k=1(1)5 (12) where the coefficients α j and β j are shown in the Table 5. 2.1. Characteristics of the method The formula in equation (8) (and its derivatives in equations (9)-(12)) is a continuous schemes associated with the linear dif- ferential operator defined by L[z(x + vkh); h] = 4∑ i=0 αkj h jz( j)(x) − 5∑ j=0 h5βiz (5)(x + v jh) ∣∣∣∣∣ k=1(1)5 (13) Expanding equation (13) in Taylor series, the constants C′i s written as linear combination of the derivatives of z(x) up to p + 1 derivative as L[z(x); h] = C0z(x)+C1hz ′(x)+C2h 2z′′(x)+· · ·+C ph pz(p)(x)+O(h( p+1)) (14) Figure 1. The region of stability where p is the order of equation (13) and consequently the formula (13). By definition, the LMM (8) is of order p if C0 = C1 = C2 = · · · = C p+4 = 0, and C p+5 , 0 in which L[z(x); h] = C p+5h p+5z(p+5)(x) + O(h(p+6)) (15) In this case, C p+5 is the principal error constant, see [29]. Definition 2.1. A linear difference operator L[z(x); h] of order p is consistent if p > 1. Thus, the order of the formula in equation (8) is p = 6 with the following error constants C p+5 = (−6.87857 × 10 −13,−2.36466 × 10−11, − 5.40035 × 10−10,−1.47456 × 10−9,−3.4408 × 10−9)T The order of the formulas in equations (9)-(12) is p = 6 and their error constants are obtained similarly. 2.2. Zero-stability and convergence A numerical method in equations (8)-(12) is zero-stable pro- vided as h → 0, the solutions is bounded. Following [20], the block method in (8)-(12) may be rewrit- ten in a matrix form as A0Yµ = A1Yµ−1 + h 5(Fµ + Fµ−1) (16) where where Yµ = ( Y 0µ, Y 1 µ, . . . , Y 5 µ )T , Yµ−1 = ( Y 0µ−1, Y 1 µ−1, . . . , Y 5 µ−1 )T 3 Olaiya et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 797 4 Table 1. Coefficients of α j, j = 0(1)4, and β j, j = 0(1)5 in equation (8) k α0 α1 α2 α3 α4 β0 β1 β2 β3 β4 β5 1 1 16 1 72 1 1296 1 31104 86197η1 58392η1 −30815η1 14415η1 −9112η1 1883η1 2 1 13 1 18 1 162 1 1944 7963η2 10528η2 −4365η2 1985η2 −1248η2 257η2 3 1 23 2 9 4 81 2 243 622η3 1392η3 −215η3 180η3 −112η3 23η3 4 1 56 25 72 125 1296 625 31104 6685η4 16600η4 −375η4 2375η4 −1368η4 275η4 5 1 1 12 1 6 1 24 401η5 1056η5 105η5 195η5 −96η5 19η5 η01 = 1 112870195200 ; η 0 2 = 1 440899200 ; η 0 3 = 2 3444525 ; η 0 4 = 625 4514807808 ; η 0 5 = 1 201600 Table 2. Coefficients of α j, j = 1(1)4, and β j, j = 0(1)5 in equation (9) k α1 α2 α3 α4 β0 β1 β2 β3 β4 β5 1 1 16 1 18 1 162 100795η 1 1 82832 1 1 −42175 1 1 19525 1 1 −12320 1 1 2543 1 1 2 1 13 1 18 1 162 2209η 1 2 3518η 1 2 −1300η 1 2 595η 1 2 −374η 1 2 77η 1 2 3 1 23 2 9 4 81 1316η 1 3 3328η 1 3 −140η 1 3 425η 1 3 −256η 1 3 52η 1 3 4 1 56 25 72 125 1296 7027η 1 4 19040η 1 4 2225η 1 4 3325η 1 4 −1712η 1 4 335η 1 4 5 1 1 12 1 6 35η 1 5 98η 1 5 25η 1 5 25η 1 5 −10η 1 5 2η 1 5 η11 = 1 4702924800 ; η 1 2 = 1 9185400 ; η 1 3 = 2 1148175 ; η 1 4 = 125 188116992 ; η 1 5 = 1 4200 ; Table 3. Coefficients of α j, j = 2, 3, 4, and β j, j = 0(1)5 in equation (10) k α2 α3 α4 β0 β1 β2 β3 β4 β5 1 1 16 1 72 40501η 2 1 42484η 2 1 −20455η 2 1 9335η 2 1 −5876η 2 1 0 2 1 13 1 18 1646η 2 2 3304η 2 2 −985η 2 2 470η 2 2 −296η 2 2 61η 2 2 3 1 13 1 9 467η 2 3 1328η 2 3 190η 2 3 205η 2 3 −112η 2 3 22η 2 3 4 1 56 25 72 497η 2 4 1444η 2 4 485η 2 4 395η 2 4 −164η 2 4 31η 2 4 5 1 1 12 222η 2 5 648η 2 5 315η 2 5 270η 2 5 −72η 2 5 17η 2 5 η21 = 1 87091200 ; η 2 2 = 1 680400 ; η 2 3 = 1 42525 ; η 2 4 = 125 3483648 ; η 2 5 = 1 8400 ; Table 4. Coefficients of α j, j = 3, 4, and β j, j = 0(1)5 in equation (11) k α3 α4 β0 β1 β2 β3 β4 β5 1 1 16 5561η 3 1 37504η 3 1 −16325η 3 1 7295η 3 1 −4576η 3 1 941η 3 1 2 1 13 1843η 3 2 5032η 3 2 −830η 3 2 515η 3 2 −328η 3 2 68η 3 2 3 1 23 254η 3 3 776η 3 3 395η 3 3 235η 3 3 −104η 3 3 19η 3 3 4 1 56 269η 3 4 800η 3 4 575η 3 4 475η 3 4 −128η 3 4 25η 3 4 5 1 1 239η34 696η 3 4 600η 3 4 555η 3 4 −24η 3 4 34η 3 4 η31 = 1 3628800 ; η 3 2 = 1 113400 ; η 3 3 = 2 14175 ; η 3 4 = 25 145152 ; η 3 5 = 1 4200 ; Table 5. Coefficients of α4 and β j, j = 0(1)5 in equation (12) . k α4 β0 β1 β2 β3 β4 β5 1 1 4991η41 12824η 4 1 −4365η 4 1 1885η 4 1 −1176η 4 1 241η 4 1 2 1 287η42 1248η 4 2 245η 4 2 45η 4 2 −32η 4 2 7η 4 2 3 1 43η43 112η 4 3 180η 4 3 155η 4 3 −48η 4 3 8η 4 3 4 1 43η44 120η 4 4 175η 4 4 225η 4 4 8η 4 4 5η 4 4 5 1 13η45 32η 4 5 55η 4 5 55η 4 5 32η 4 5 13η 4 5 η41 = 1 86400 ; η 4 2 = 1 5400 ; η 4 3 = 1 675 ; η 4 4 = 5 3456 ; η 4 5 = 1 200 ; Y 0µ = (yn+ 16 , yn+ 13 , yn+ 23 , yn+ 56 , yn+1) T ... Y 5µ = (y (v) n+ 16 , y(v) n+ 13 , y(v) n+ 23 , y(v) n+ 56 , y(v)n+1) T Y 0µ−1 = (yn− 56 , yn− 23 , yn− 13 , yn− 16 , yn) T ... Y 5µ−1 = (y (v) n− 56 , y(v) n− 23 , y(v) n− 13 , y(v) n− 16 , y(v)n ) T Fµ = ( fn+ 16 , fn+ 13 , fn+ 23 , fn+ 56 , fn+1) T Fµ−1 = ( fn− 56 , fn− 23 , fn−13 , fn− 16 , fn) T Hence, as h → 0 the method in equation (16) becomes A0Yµ = A1Yµ−1 (17) where A0 is the identity matrix of order 25, A0 = I25, and A1 is 4 Olaiya et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 797 5 Table 6. Absolute Error for Problem 1 x = 1.0 x = 1.5 t 1SHBI mVIA-I 1SHBI mVIA-I 0.01 0.00000 0.00000 2.14572 × 10−18 0.00000 0.02 1.11257 × 10−18 8.88178 × 10−16 2.22141 × 10−18 8.88178 × 10−16 0.03 8.47894 × 10−17 1.19904 × 10−14 4.71125 × 10−17 1.95399 × 10−14 0.04 5.41381 × 10−17 8.79296 × 10−14 3.12412 × 10−17 1.43884 × 10−13 0.05 9.12414 × 10−16 4.19229 × 10−13 1.49787 × 10−17 6.90114 × 10−13 Comparing absolute errors of 1SHBI with the mVIA-I in [11] for Example 1. Table 7. Error for Example 2 x yex yapprox Error 0.12566 -0.07426755 -0.07426785 2.9720E-7 0.25132 0.05130957 0.05130487 4.7001E-6 0.31415 0.11392287 0.11391146 1.1407E-5 0.43982 0.23757397 0.23753066 4.3304E-5 0.50265 0.29812884 0.29805541 7.3430E-5 0.62831 0.41551891 0.41534181 1.7710E-4 0.75398 0.52644076 0.52607803 3.6273E-4 0.81681 0.57893577 0.57843927 4.9650E-4 0.94247 0.67698465 0.67611561 8.6903E-4 1.00530 0.72216309 0.72104522 1.1178E-3 0 ≤ x ≤ 2π, t = 1, h = 0.0628319. Table 8. Maximum Error for Problem 2 at t = 1 Method N L1 L2 L∞ DGFEM 10 0.11E-1 0.12E-1 0.17 20 0.39E-2 0.43E-2 0.61E-2 40 0.12E-3 0.14E-3 0.19E-3 80 0.36E-5 0.40E-5 0.57E-5 1SHBI 10 1.52E-6 3.23E-6 1.17E-7 20 2.15E-8 3.24E-6 3.21E-8 40 5.18E-8 2.79E-9 5.27E-8 80 2.32E-10 4.71E-10 8.11E-10 DGFEM is Discontinuous Galerkin Finite Element Method developed in [32]. The p-norm in Table 8 is given as Lp = ||yi − y(xi)||p =  inf∑ i=1 |yi − y(xi)| p  1 p L∞ = ||yi − y(xi)||∞ = max 1≤i≤N {|yi − y(xi)|} a 25 × 25 matrix given by A11 A22 A33 A44 A55  with the A11, . . ., A55 being 5 × 5 matrices respectively, given yexact ynumerical Error Figure 2. The shaded regions shows the surface plots for the numerical solution, the analytic solution and the residue (error) for Example 1. by Aii =  0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0  , i = 1, . . . , 5 5 Olaiya et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 797 6 Table 9. Numerical Results with t = 1 for Example 3 x Exact Approximate Error 0.1 1.999999999998E-10 1.999999999998E-10 0.000000000000000 0.2 1.999999999992E-10 1.999999999991E-10 1.292469707114105E-25 0.3 1.999999999982E-10 1.999999999981E-10 3.618915179919496E-25 0.4 1.999999999968E-10 1.999999999967E-10 6.720842476993354E-25 0.5 1.999999999950E-10 1.999999999949E-10 1.214921524687259E-24 0.6 1.999999999928E-10 1.999999999927E-10 1.757758801675183E-24 0.7 1.999999999902E-10 1.999999999901E-10 2.429843049374518E-24 0.8 1.999999999872E-10 1.999999999871E-10 2.998529720504725E-24 0.9 1.999999999838E-10 1.999999999837E-10 3.127776691216136E-24 1.0 1.999999999800E-10 1.999999999799E-10 2.403993655232236E-24 Table 10. Maximum Error for Example 3 at t = 1 Method GA with RK MQ with RK IMQ with RK 1SHBI L2 1.9774E-21 5.9692E-12 1.9774E-21 5.96847E-24 L∞ 1.2705E-21 3.2896E-12 1.2705E-21 3.12778E-24 The matrices Aii have the characteristic polynomial |A j j−λI5| = 0, for j = 1, . . . , 5, that is, λ4(λ − 1) = 0. The characteristic polynomial has the root λr = 0, for r = 1, . . . , 4 and λ5 = 1. The method is zero-stable, since the roots of the characteristic polynomial have one unity while others are zero (see [29]). For convergence, the following theorem apply. Theorem 2.1. [30]. A linear multistep method is convergent provided it is consistent (having order p ≥ 1) and zero-stable. The derived method has p = 6, and equally zero-stable and hence it is convergent. 2.3. Linear stability analysis The linear stability for any given h > 0 is concern with the behaviour of the underlined problem not just the numerical method. Here, the stability properties for the intending numer- ical method is analyzed by considering the linear test equation for µ > 0 of the form y(v) = −µ5y (18) the test in equation (18) is appropriate since it has a bounded solution as µ → 0. Here, µ is the frequency. set δ = µh and then applying to the test equation in (18), and after some manipula- tions, the following equation results Zµ = M(δ)Zµ−1, δ = µh (19) where M(δ) = A0 + δB0 (A1 −δB1) is the required stability matrix. The amplification matrix in equation (19) results on the domi- nant eigenvalues given as M(δdominant) = 6(−2)4/531/5 ( −1 − 4δ1/6 + 5δ1/3 − 5δ2/3 + 4δ5/6 −δ )1/5 ( 11 − 56δ1/6 + 285δ1/3 + 285δ2/3 − 56δ5/6 + 11δ )1/5 (20) having the stability region in the Figure 1. These roots (containing the real and imaginary parts) are plotted and as shown in Figure 1. Here we study the bounded- ness of the solution under consideration through the eigenval- ues of the stability matrix M(δ) for which these eigenvalues δ is such that |δ| < 1 for the derived method to be stable. If δ is real, then the absolute stability region is reduced to a real interval which is called an interval of stability, see [31]. Figure 1 shows the stability region for the proposed method, with the stability interval (0, 8.7893). 2.4. Implementation The system formed by the semi-discretization given by equa- tion (4) is solved using the unified block scheme formed by equations (8)-(12) with 5N equations and 5N unknowns solve simultaneously, whose solution provides a set of approximate values of (1) using codes written in Mathematica 12.0, enhanced by the feature NSolve[] for linear problems while nonlinear problems were solved by Newton’s method enhanced by the feature FindRoot[]. Following [20], the following algorithm summarizes the computational procedures. We begin by noting that the solution of the problem in equation (1) is sought in the subintervals DN = a = x0 < x1 < .. . < xN = b and DM = c = t0 < t1 < .. . < tM = d, where h = b−a N , k = d−cM are constant step-size. Step 1: Use the block method setting n = 0, m = 0, to obtain V1 on the rectangle [y0,m, y1,m](n,m)∈[a,b]×[c,d], similarly, for, n = 1 so that V2 is obtained on the rectangle [y1,m, y2,m](n,m)∈[a,b]×[c,d], and on the rectangle [y3,m, y4,m](n,m)∈[a,b]×[c,d] . . . [yn=N−1,m, yn=N,m](n,m)∈[a,b]×[c,d] for m = 0, 1, 2, . . . , M we thus obtain V3, V4, . . . , VD. Step 2: Solve the unified block given by the system V1 ⋃ V2 ⋃ , · · · , VD obtained in step 1. Step 3: The solution of equation (1) is approximated by the solutions in step 2 as yn,m = [y(x1, t); y(x2, t) . . . y(xn, t)]T for t > 0, n = 1, 2, . . . N. 6 Olaiya et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 797 7 yexact ynumerical Error Figure 3. Surface plots showing the numerical solution, the analytic solution and the residue for Example 2. 3. Numerical Examples In this section, we test the efficiency of the derived method and thus compare only with the exact solution of the given prob- lem extracted from literature. Example 1.. Consider the fifth order KdV equation, yt + yyx − yyxxx + yxxxxx = 0 y(x, 0) = ex, } (21) with exact solution y(x, t) = ex−t. After discretization of the ”t” variable, we obtain, ym+1 − ym−1 (2∆t) + ym dym d x − ym d3ym d x3 + d5ym d x5 = gm, x ∈ [0, 1] m = 1, . . . M − 1 (22) Figure 4. Surface plots for the numerical solution for Example 4 where ∆t, tm, m = 0, 1, . . . , M, y, ym(x) ≈ y(x, tm), and gm = 0, expressed as y(v) = f (x, y, y′, y′′′) = Ay + g (23) A is a k by k matrix. To show the efficiency of 1SHB1, the above Table 6 shows the absolute error for different values of t the values x = 1.0 and 1.5 respectively. It can be observe that the 1SHBI outperformed mVIA-I for the example considered. The Figure 2 shows a good agreement of the numerical and exact solutions. Example 2.. Consider a time dependent biharmonic fifth order equation discussed in [32]. yt + yx + yxxxxx = 0, 0 ≤ x ≤ 2π, t ≥ 0 y(x, 0) = sin (x), y(0, t) = y(2π, t)  (24) The analytic solution for this problem is y(x, t) = sin(x − 2t). Upon discretization of the time variable, we obtain, ym+1 − ym−1 (2∆t) + dym d x + d5ym d x5 = gm, 0 ≤ x ≤ 1, m = 1, . . . M − 1 (25) 7 Olaiya et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 797 8 where ∆t, tm, m = 0, 1, . . . , M, y, ym(x) ≈ y(x, tm), g and gm are expressed in the form y(v) = f (x, y, y′, y′′, y′′′, y(iv)) = Ay + g (26) A is a k × k matrix (k = (N − 1)(M − 1)) and gm = 0. Table 7 compares the errors obtained for Example 2. Figure 3 shows the representation of the numerical solution, analytical solution and residue (errors), for Example 2. Table 8, for different subinterval N, shows the maximum errors L∞ and the Lp with p = 1, 2 − norm obtained, in compari- son with the 1SHBI and the method in [32]. This shows the superiority of the 1SHBI. Example 3.. Consider the nonlinear fifth order KdV equation called Lax’s cases of generalized KdV equation discussed [33]. yt + 45y2yx + 15yxyxx + 15yyxxx + yxxxxx = 0, 0 ≤ x ≤ 1, t ≥ 0 y(x, 0) = 2k2 sec h2(k(x − x0))  (27) The exact solution for this problem is y(x, t) = 2k2 sec h2(k(x − 16k4t − x0)) Upon discretization of the time variable, we obtain, ym+1 − ym−1 (2∆t) + 45ymym dym d x + 15 dym d x d2ym d x2 + 15ym d3ym d x3 + d5ym d x5 = gm, 0 ≤ x ≤ 1, m = 1, . . . M − 1 (28) where ∆t, tm, m = 0, 1, . . . , M, y, ym(x) ≈ y(x, tm), g and gm are expressed in the form y(v) = f (x, y, y′, y′′, y′′′, y(iv)) = Ay + g (29) A is as expressed in Example 1 and gm = 0. In [33], the authors presented a numerical solution of equa- tion (27) using a meshless method of lines. This method uses Meshless, Multiquadric (MQ), Inverse multiquadric (IMQ) and Gaussian (GA) as Radial basis function (RBF) for spatial deriva- tives and Runge-Kutta method as a time integrator. The constant step-size used for Table 9 and Table 10 is h = 0.1. Figure 4 shows the graphical representation with surface plot for the numerical solution (shaded region), analytical so- lution (shaded region) and residue or error (shaded region), for Example 3. The method presented in [33] for the numerical solution of Example 4 uses a meshless method of lines. This method uses Meshless, Multiquadric (MQ), Inverse multiquadric (IMQ) and Gaussian (GA) as Radial basis function (RBF) for spatial deriva- tives and Runge-Kutta method as a time integrator. 4. Conclusion In this work, a one step hybrid block integrator (ISHBI) was derived consisting of continuous linear multistep methods. This was used to solve certain fifth- order PDEs subject to appro- priate initial-boundary conditions. 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