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Collocation method for Convection-Reaction-Diffusion equation

Department of Mathematics, Central Tehran Branch, Islamic Azad University, Tehran, Iran

⁎Corresponding author. rashidinia@iust.ac.ir (Jalil Rashidinia)

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

A collocation method based on B-spline is developed for solving Convection-Reaction-Diffusion equation subjected to Dirichlet’s boundary conditions. The method comprises an explicit finite difference associated with extended cubic B-spline collocation method. We analyze the convergence and stability of the presented method. The proposed method is applied to various test examples and results are reported in Tables. The obtained numerical results have been compared with the results of the existing methods. Numerical results verify the efficiency and applicability of the scheme.

Keywords

65M06
65M12
65M15
65M70
Convection-Reaction-Diffusion equation
Redefined extended cubic B-spline
Stability and convergence analysis
PubMed
1

1 Introduction

In this work, we consider the following one-dimensional parabolic Convection-Reaction-Diffusion equation:

(1)
Hu=g(u), where H is defined as Hu=Dt+Dxu, and Dtu(x,t)=tu(x,t), Dxu(x,t)=a(x,t)x-b(x,t)2x2u(x,t),(x,t)[c,d]×[t0,T], with the initial condition
(2)
u(x,t0)=f(x),cxd,
and Dirichlet boundary conditions
(3)
u(c,t)=Q0(t),u(d,t)=Q1(t),t0tT
where u(x,t) is the unknown quantity being investigated. a(x,t) is the velocity of the medium which is called convection velocity, b(x,t) is the diffusion coefficient and g(u) is reaction source (Makungu et al., 2012).

The application of Convection-Reaction-Diffusion equation (CRD) can be classified into three processes: The first process is Convection which is due to the movement of materials from one region to another, the second process is Reaction which is due to decay, adsorption and reaction of substances with other components and the last process is Diffusion which is due to the movement of materials from high concentration to the low region. Qualitatively all the three processes from CRD model that describe how to disturbed quantity being studied in the medium changes (Makungu et al., 2012).

The Convection- Reaction- Diffusion partial differential equation provides very useful mathematical models in applied sciences such as physics, biology, hydrology and, engineering (Morton, 1996). The descriptions of Eq. (1) includes the transport chemistry in the atmosphere (McRea et al., 1982), heat transfer in a draining film (Isenberg and Gutfinge, 1972), finance (Wilmott et al., 1993), fluid flow (Cengel and Cimbala, 2006; Roache, 1972), hydrology (Cunningham et al., 1991), modelling of biological systems and population dynamics (Murray, 1989; Witelski, 1997).

During past years, many researchers paid attention to analysis, improvement, and implementation of the stable method for numerical solutions of nonlinear Convection-Reaction-Diffusion, see for example (Kaya, 2015).

A new two-level implicit difference method of order O( k2 + kh2 + h4 ) based on three spatial grid points and arithmetic average discretization was applied by Mohanty et al. (1990), Mohanty et al. (2007) to determine the solution of one-dimensional quasi-linear and nonlinear parabolic partial differential equations, respectively.

In Duan et al. (2012), Hsieh and Yang (2016), Theeraek et al. (2011) authors proposed several finite element methods for approximation the solution of CRD equation. The Discontinuous Galerkin method has been applied for solving nonlinear CRD equation in Uzunca et al. (2014), Yucel et al. (2013). Monotone iterative methods for finding solution of CRD equation and improving the rate of convergence is suggested in Wang (2011). In Cui (2015) High order Compact exponential method has been used to solve fractional CRD equation with variable coefficients. Nonstandard finite difference combined with tension spline to determine the solution of CRD equation is used in Rashidinia and Shekarabi (2016). In Rashidinia and Sharifi (2016), Raslan et al. (2010) redefined extended B-spline collocation and quintic B-spline finite element method has been applied for solution of the partial differential equation.

In this paper, we develop the collocation method using a combination of finite difference and extended B-spline function for the solution of one-dimensional CRD equation. This article is arranged as follows: In Section 2, the description of the method is explained. Section 3, is devoted to prove the convergence and stability of the method. In Section 4, numerical illustrations are included to verify the accuracy and effectiveness of the presented approach. The paper ends with a brief conclusion.

2

2 Description of the method

2.1

2.1 Temporal discretization

In this section, we denote Δ be a uniform partition of the domain [c,d]×[t0,T] , where xj=c+jh,j=0,,N and tn=t0+nk,n=0,1,2, .

Considering the finite difference operator

(4)
utnδtk(1-γδt)un,γ1, by discretizing time variable and substituting the operator (4) into Eq. (1), we obtain: δtk(1-γδt)un+a(x,tn)uxn-b(x,tn)uxxn=g(un), so we have
(5)
δtun+a(x,tn)k(1-γδt)uxn-b(x,tn)k(1-γδt)uxxn=k(1-γδt)g(un).
By using some algebraic manipulations, we can obtain the following differential equation
(6)
bûxx-aûx+1γkû+g(û)=q̂(x),
associated with boundary conditions,
(7)
û(c)=Q0(t),û(d)=Q1(t),
where, ûun+1,ûx(ux)n+1,ûxx(uxx)n+1,g(û)=g(x,tn,un+1),b(x,tn)=b,a(x,tn)=a,q̂(x)=b1+γγuxxn-a1+γγuxn+1γkun+1+γγg(un), g(û) can be linear or nonlinear function.

For starting the computations we must use the initial condition u0=u(x,0)=f(x) by Taylor’s series expansions of u at t=t0+k we have:

(8)
u1=u0+kut0+k22!utt0+O(k3). Via differentiating the initial condition with respect to x, we can achieve ux,uxx,uxxx, at t=t0 , by considering Eq. (1) we have,
(9)
ut0=[buxx-aux+g(u)]0.
By differentiating (9) with respect to x we obtain,
(10)
uxt0=[buxxx-auxx+gx+guux]0,uxt0=[buxxx-auxx+gx]0,
similarly differentiating (9) with respect to t and using the Eq.(10) we have,
(11)
utt0=[buxxt-auxt+gt+guut]0,utt0=[buxxt-auxt+gt]0,
substituting (2), (9),(11) into (8) we can compute u1 in the following forms:
(12)
u1=f(x)+k[buxx-aux+g(u)]0+k22![buxxt-auxt+gt]0+O(k3),
and
(13)
u1=f(x)+k[buxx-aux+g(u)]0+k22![buxxt-auxt+gt+guut]0+O(k3).
Now by using Eqs. (12) and (13) for linear function g(û) and nonlinear function g(û) respectively, we can start the processes of our scheme (6).
Theorem 2.1

The time discretization steps (4)–(6) give the second order convergence.

Proof

Suppose û(ti) be the exact and ûi be the approximate solution of the Eq. (1) at ith time level and also assume that ei be the local truncation error in (6) as ei=ûi-û(ti) , by considering the operator (1-γδt) in Eq. (4) and applying Taylor’s series expansion we have:

(14)
|ei|νik3, for γ=-12 , where νi is finite constant independent of k.

Let En+1 be the global error then En+1=i=1nei,(kTn) , therefore by applying (14) we obtain: |En+1|=i=1neii=1n|ei|i=1nνik3n.νk3νnTnk2=ϑk2, where ϑ=νT , which concludes the proof of Theorem 2.1. □

2.2

2.2 Redefined extended cubic B-spline

In this section, we apply redefined extended B-splines collocation method to approximate solution of Eqs. (6) and (7). We consider Δ={c=x0<<xN=d} be a uniform partition of the interval [c,d] by the knots xj with h=c-dN .

The extended cubic B-spline Bj(x,λ) is defined as:

(15)
Bj(x,λ)=124h44h(1-λ)(x-xj-2)3+3λ(x-xj-2)4,xj-2<xxj-1,(4-λ)h4+12h3(x-xj-1)+6h2(2+λ)(x-xj-1)2-12h(x-xj-1)3-3λ(x-xj-1)4,xj-1<xxj,(4-λ)h4+12h3(xj+1-x)+6h2(2+λ)(xj+1-x)2-12h(xj+1-x)3-3λ(xj+1-x)4,xj<xxj+1,4h(1-λ)(xj+2-x)3+3λ(xj+2-x)4,xj+1<xxj+2,0,otherwise. The extended B-spline function has one arbitrary parameter λ , when λ tends to zero the extended B-spline reduced to convectional B-spline function. The extended B-spline has the properties such as: local support, non-negativity, partition of unity and C2 continuity, the parameter λ control the tension of the solution curve (Xu and Wang, 2008).

We focus on developing the collocation method to approximate the solution of Eqs. (1)–(3). Let U^(x,t) and û(x,t) are the approximate solution and exact solution of the problems (1)–(3) respectively. We describe the approximate solution at the boundary points in the following form: Rashidinia and Sharifi (2016)

(16)
U^(x,t)=j=-1N+1ĉjBj(x,λ)=B-1(x,λ)B-1(x0,λ)Q0(t)+BN+1(x,λ)BN+1(xN,λ)Q1(t)+j=0NĉjB^j(x,λ), where B-1(x,λ)B-1(x0,λ)Q0(t)+BN+1(x,λ)BN+1(xN,λ)Q1(t)=W(x,t) is weight function that takes care of the given boundary conditions, also we define the functions B^j(x,λ) as follows:

B^j(x,λ)=Bj(x,λ)-Bj(x0,λ)B-1(x0,λ)B-1(x,λ),j=0,1,

B^j(x,λ)=Bj(x,λ),j=2,,N-2,

B^j(x,λ)=Bj(x,λ)-Bj(xN,λ)BN+1(xN,λ)BN+1(x,λ),j=N-1,N.

B^j(x,λ),j=0,,N is as the new set of redefined extended cubic B-spline functions which vanish on the Dirichlet’s boundary conditions. Suppose U^(x,t) satisfies the Eq. (6) associated with boundary conditions (7), so we obtain

(17)
HU^(xj,t)=q̂(xj),0jN,
(18)
U^(x0,t)=Q0(t),U^(xN,t)=Q1(t),
where Hû=bûxx-aûx+1γkû+g(û) . By applying Eq. (16) in Eqs. (17) and (18) we proceed as follows:
(19)
bj=0NĉjB^j(x,λ)+Wxx(x,t)-aj=0NĉjB^j(x,λ)+Wx(x,t)+1γkj=0NĉjB^j(x,λ)+W(x,t)-gxj,j=0NĉjB^j(x,λ)+W(x,t)=q̂(xj),0jN.
By using the properties of extended cubic B-spline function in Eq. (19), we can obtain the following linear or nonlinear system of equations,
(20)
AC^+h2G^=h2ϕ̂,A=z00000xyz000xyz00000xyz0000z1,
where, z0=-12b2+λ4-λ-ah8+λ4-λ,z1=-12b2+λ4-λ+ah8+λ4-λ, x=b(2+λ)2+ah2+h2γk4-λ24,y=-b(2+λ)+h2γk8+λ12, z=b(2+λ)2-ah2+h2γk4-λ24, and G^ can be as linear or nonlinear term G^=ĝ0ĝ1ĝN, where, ĝi=ĝxi,4-λ24ĉi-1+8+λ12ĉi+4-λ24ĉi+1, C^=ĉ0ĉ1ĉN,h2ϕ̂=h2q̂0-12b(2+λ4-λ)-12ah(14-λ)+h2γkQ0(t)h2q̂1h2q̂N-1h2q̂N-12b(2+λ4-λ)-12ah(14-λ)+h2γkQ1(t).

3

3 Stability and convergence analysis

3.1

3.1 Stability analysis

In this section, we will prove the stability and convergence analysis of our scheme for solution of problem (1) associated with boundary conditions (2) and (3).

We prove the stability analysis by using the Von-Neumann stability method. The homogeneous part of the Eq. (6) is as follows

(21)
1γkujn+1-a(ux)jn+1+b(uxx)jn+1=1γkujn-a1+γγ(ux)jn+b1+γγ(uxx)jn. In Eq. (21) u,ux,uxx are replaced by the values of extended cubic B-spline functions, so we obtain
(22)
x(C^)j-1n+1+y(C^)jn+1+z(C^)j+1n+1=p(C^)j-1n+q(C^)jn+r(C^)j+1n,
where, x=b(2+λ)2+ah2+h2γk4-λ24,y=-b(2+λ)+h2γk8+λ12, z=b(2+λ)2-ah2+h2γk4-λ24,p=b(2+λ)21+γγ+ah21+γγ+h2γk4-λ24, q=-b(2+λ)1+γγ+h2γk8+λ12,r=b(2+λ)21+γγ-ah21+γγ+h2γk4-λ24.

Now we consider the trial solution at the mesh point (xj,tn) as: (C^)jn=ξnexp(iθjh), here i=-1 and θ is real.

By using (C^)jn=ξnexp(iθjh) in Eq. (22) and simplifying we have

(23)
ξ=pexp(-iθh)+q+rexp(iθh)xexp(-iθh)+y+zexp(iθh), by substituting the values of x,y,z,p,q,r in (23), we get
(24)
ξ=-b(1+γγ)(2+λ)(1-cosβ)+h212γk2λsin2β2+4(1+2cos2β2)-iah(1+γγ)sinβ-b(2+λ)(1-cosβ)+h212γk2λsin2β2+4(1+2cos2β2)-iahsinβ,
here we have taken, θh=β .

The simplified form of Eq. (24) can be written as:

(25)
ξ=1+γγX1+(γ1+γ)X2-iY1X1+X2-iY1, where, X1=-b(2+λ)(1-cosβ),X2=h212γk2λsin2β2+4(1+2cos2β2),Y1=ahsinβ. By substituting 1+γγ=α and cosβ=μ in Eq. (24), we have:
(26)
ξ=α-b(2+λ)(1-μ)+h212γkαλ(1-μ)+4(2+μ)-iah1-μ2-b(2+λ)(1-μ)+h212γkλ(1-μ)+4(2+μ)-iah1-μ2,|ξ|2=α2-b(2+λ)(1-μ)+h212γkα(λ(1-μ)+4(2+μ)2+a2h2(1-μ2)-b(2+λ)(1-μ)+h212γk(λ(1-μ)+4(2+μ)2+a2h2(1-μ2),
for all θ and λ-2 , the numerator in Eq. (26) is less than denominator, therefore |ξ|1 , thus the proposed method is unconditionally stable.

3.2

3.2 Convergence analysis

By following Henrici (1962), we want to prove the convergence of our method for the nonlinear function g(u) . For this purpose, the following Lemma and Theorem are required.

Lemma 3.1

Let {B-1(x,λ),,BN+1(x,λ)} be the set of extended B-splines, which the Bi(x,λ) satisfy in the following inequality:

(27)
j=-1N+1Bj(x,λ)74,x0,1.
Proof

For the proof see Rashidinia and Sharifi (2016). □

Theorem 3.1

Let û(x)C4[c,d],Δ be the partition of [c,d] and U(x) be the B-spline interpolation function û(x) , we have:

(28)
Di(û-U)φih4-i,i=0,,3.
Proof

For the proof see Hall (1968). □

Theorem 3.2

Suppose û(x) be the exact solution of (6) and U^(x) be the extended B-spline approximate solution of û(x) then the error bound in the solution is:

û(x)-U^(x)βh2,β=φ0h2+74R2 .

Proof

Let U^(x) be the unique extended B-spline approximate solution of û(x) , suppose U(x) be the computed extended B-spline approximate solution of U^(x) as follows: U^(x)=j=-1N+1ĉjBj(x,λ), U(x)=j=-1N+1cjBj(x,λ), by substituting U(x) into (20) we get

(29)
AC+h2G=h2ϕ,
where, G=g0g1gN,C=c0c1cN,h2ϕ=h2q0-12b(2+λ4-λ)+12ah(14-λ)+h2γkQ0(t)h2q1h2qN-1h2qN-12b(2+λ4-λ)-12ah(14-λ)+h2γkQ1(t). By subtracting (20) from (29) we have,
(30)
A(C-C^)+h2(G-G^)=h2(ϕ-ϕ̂),
the bound on ϕ-ϕ̂ can be obtained by using Theorem 3.1 By applying (17) we can obtain: q(xj)-q̂(xj)|=|HU(xj)-HU^(xj)|=|bU(xj)-Û(xj)+aU(xj)-Û(xj)+1γkU(xj)-U^(xj)+gxj,U(xj)-ĝxj,U^(xj), therefore we have,
(31)
q(xj)-q̂(xj)bU(xj)-Û(xj)+aU(xj)-Û(xj)+1γkU(xj)-U^(xj)|+|gxj,U(xj)-ĝxj,U^(xj).
From the Eq. (31) and using Theorem 3.1, we can obtain,
(32)
ϕ-ϕ̂bφ2h2+aφ1h3+1γkφ0h4+R|U(xj)-U^(xj)|bφ2h2+aφ1h3+1γkφ0h4+Rφ0h4,
where g(z)R,zR3 . By using the Eq. (32) we can obtain:
(33)
ϕ-ϕ̂R1h2,R1=bφ2+aφ1h+φ0h21γk+R.

Now the bound on h2(G-G^) is, h2(G-G^)=h2gx0,Q0(t)gxi,4-λ24ci-1+8+λ12ci+4-λ24ci+1gxN,Q1(t)-ĝx0,Q0(t)ĝxi,4-λ24ĉi-1+8+λ12ĉi+4-λ24ĉi+1ĝxN,Q1(t), by using the mean value theorem we have the following relation,

(34)
h2(G-G^)=h2gu(ζ1)L(C-C^), where ζ1(0,1) and L is defined as: L=004-λ248+λ124-λ244-λ248+λ124-λ2400, substituting (30) into (34) we get
(35)
F(C-C^)=h2(ϕ-ϕ̂),
where F=A+h2gu(ζ1)L . The matrix F, for λ-2 is a strictly diagonally dominant matrix so it is non-singular, thus we can rewrite (35) in the following form:
(36)
(C-C^)=h2F-1(ϕ-ϕ̂),
by taking norm from (36) we get
(37)
C-C^h2F-1ϕ-ϕ̂h2F-1h2R1=h4R1F-1.

Now we calculate the sum of each row of matrix F, let that χj,0jN is the summation of the jth row of the matrix F=[fj,i](N+1)×(N+1) , then we get the following relations:

(38)
χ0=i=0Nf0,i=-12bh22+λ4-λ-ah8+λ4-λ,j=0,
(39)
χj=i=0Nfj,i=1γk+h2gu,1jN-1,
(40)
χN=i=0NfN,i=-12bh22+λ4-λ+ah8+λ4-λ,j=N.

Noticing to the theory of matrices Varga (1962), we have:

(41)
j=0Nfl,j-1χj=1,l=0,,N, where fl,j-1 are the elements of F-1 , we have
(42)
F-1=j=0N|fl,j-1|1minχj=1h2σ1h2|σ|,0jN.
By substituting (42) into (37) we get,
(43)
C-C^R1h4h2|σ|R2h2,R2=R1|σ|.
Now we have:
(44)
U(x)-U^(x)=j=-1N+1(cj-ĉj)Bj(x,λ),
by taking norm from (44) and using (43) and (27), we obtain
(45)
U(x)-U^(x)=j=-1N+1(cj-ĉj)Bj(x,λ)|j=-1N+1Bj(x,λ)|cj-ĉj74R2h2.
By using Theorem 3.1 we have:
(46)
û(x)-U(x)φ0h4,
by using Eqs. (45) and (46) we get û(x)-U^(x)û(x)-U(x)+U(x)-U^(x)φ0h4+74R2h2=βh2, where β=φ0h2+74R2 . □

If we assume u(x,t) be the exact solution of Eq. (1) and U(x,t) be the numerical approximation, then we have:

u(x,t)-U(x,t)ρ(k2+h2) ,   ρ=Max{φ0h2+74R2,ϑ} , where ρ is a constant.

4

4 Numerical illustrations

In this section, we consider five examples of linear and non-linear Convection-Reaction-Diffusion equation. Our numerical results are compared with results in Biazar and Mehrlatifan (2018), Dehghan (2004), Ismail et al. (2004), Macias Diaz and Puri (2012), Mittal and Jain (2012), Rashidinia and Shekarabi (2016). The absolute errors in the solutions are tabulated in Tables 1–6. Our results demonstrate the accurate nature of the proposed method.

Example 1

Consider the following linear Convection-Reaction-Diffusion equation (Ismail et al., 2004): ut+aux=b2ux2,x[0,1],t0,

with initial and boundary conditions u(x,0)=exp(γx),u(0,t)=exp(δt),u(1,t)=exp(γ+δt). The exact solution is given by u(x,t)=exp(γx+δt) .
Table 1 Maximum absolute error for example 1.
x Method in Ismail et al. (2004)
t=1 t=2 t=5
0.10 2.56(-10) 2.38(-10) 5.65(-10)
0.50 8.93(-10) 1.38(-9) 1.91(-9)
0.90 1.33(-9) 2.83(-9) 3.97(-9)
x Douglas method Rashidinia and Shekarabi (2016)
t=1 t=2 t=5
0.10 2.56(-7) 2.37(-7) 5.63(-7)
0.50 8.37(-7) 1.38(-6) 1.90(-6)
0.90 1.33(-6) 2.82(-6) 3.95(-6)
x Present method (λ=-2)
t=1 t=2 t=5
0.10 1.99181(-11) 1.86257(-11) 6.75869(-11)
0.50 6.85145(-11) 6.69412(-11) 4.78064(-11)
0.90 4.00414(-10) 4.96767(-9) 1.33356(-9)
Table 2 Maximum absolute error for different values of λ for example 1.
x λ=0 λ=-1.5 λ=-2
0.1 6.95357(-7) 8.91931(-6) 6.75898(-9)
0.2 1.86257(-7) 4.83274(-6) 6.73565(-9)
0.3 4.96767(-8) 2.50392(-6) 5.75884(-9)
0.4 1.24526(-8) 1.08594(-6) 5.65548(-9)
0.5 1.33356(-8) 6.29531(-8) 4.75869(-9)
0.6 1.19181(-8) 9.36954(-7) 6.41047(-9)
0.7 4.78064(-8) 2.27749(-6) 8.60556(-9)
0.8 1.79305(-7) 4.44594(-6) 5.84587(-9)
0.9 6.69412(-7) 8.23082(-6) 3.75839(-9)
Table 3 Maximum absolute error for example 2.
x Method in Dehghan (2004) Method in Mittal and Jain (2012) Present method (λ=-2)
t=1 t=1 t=1
0.10 9.06(-10) 9.96(-9) 9.79263(-10)
0.20 1.54(-9) 1.91(-8) 9.03905(-9)
0.30 1.84(-9) 2.70(-8) 8.62793(-9)
0.40 1.77(-9) 3.33(-8) 9.20736(-9)
0.50 1.33(-9) 3.78(-8) 8.45641(-9)
0.60 5.59(-10) 4.02(-8) 9.37931(-10)
0.70 3.83(-10) 3.99(-8) 8.28461(-10)
0.80 1.18(-9) 3.60(-8) 9.54806(-9)
0.90 1.31(-9) 2.55(-8) 8.11957(-10)
Table 4 Maximum absolute error for example 3.
x Method in Rashidinia and Shekarabi (2016) Present method
δ=1,a=100 δ=100,a=5 δ=1,a=100 δ=100,a=5
0.10 5.41124(-8) 1.38435(-3) 7.21942(-8) 2.91738(-6)
0.20 3.53667(-7) 2.85513(-4) 5.11234(-7) 1.84315(-6)
0.30 7.22626(-7) 5.86763(-5) 8.33893(-7) 3.25879(-6)
0.40 1.20347(-6) 1.02727(-5) 2.25439(-7) 2.46877(-6)
0.50 1.71858(-6) 2.48386(-6) 3.65431(-7) 3.71574(-6)
Table 5 Maximum absolute error for example 4.
x Method in Mittal and Jain (2012) Present method
t=1 t=2 t=1 t=2
0.10 1.06(-6) 1.01(-13) 6.83553(-7) 7.56433(-13)
0.20 5.02(-6) 3.65(-12) 6.52334(-7) 7.01161(-13)
0.30 1.82(-5) 7.56(-11) 6.65116(-7) 6.91534(-12)
0.40 1.08(-5) 1.06(-9) 6.98728(-7) 6.463282(-11)
0.50 4.63(-5) 1.04(-8) 7.22451(-7) 1.38677(-9)
0.60 4.17(-6) 7.27(-8) 7.41511(-7) 1.12578(-9)
0.70 3.78(-5) 3.53(-7) 7.39468(-7) 1.01969(-9)
0.80 7.10(-6) 1.14(-6) 6.93217(-7) 2.00434(-8)
0.90 8.98(-6) 2.12(-6) 6.10194(-7) 1.49526(-8)
Table 6 Maximum absolute error for example 5.
Method in Biazar and Mehrlatifan (2018) Method in Macias Diaz and Puri (2012) Present method
h=0.0125,k=0.001 1.09(-4) 3.1835(-2) 1.25216(-6)
h=0.025,k=0.0001 2.8(-3) 3.1835(-2) 1.9957(-6)

The absolute errors in the solutions for different time levels with a=3.5,b=0.022,γ=0.02854797991928,δ=-0.0999,h=0.01 and k=0.001 are tabulated in Table 1, and compared with the results (Ismail et al., 2004), these results verify the accurate value of our scheme. The maximum absolute errors in the solution for different λ , with t=2,h=0.1 and k=0.01 , are tabulated in Table 2. We observe that, the different values of λ , satisfied in the condition λ-2 .

Example 2

Consider the following linear Convection-Reaction-Diffusion equation (Dehghan, 2004): ut+aux=b2ux2,x[0,1],t0, with initial and boundary conditions u(x,0)=exp-(x-2)28,u(0,t)=2020+texp(2+0.8t)20.4t+8,u(1,t)=2020+texp(1+0.8t)20.4t+8 .

The exact solution is given by u(x,t)=2020+texp-(x-2-0.8t)20.4t+8 .

The absolute errors in the solutions with a=0.8,b=0.1,h=0.01,k=0.001 and in time t=1 are tabulated in Table 3, and compared with the results in Dehghan (2004), Mittal and Jain (2012), these results verify the accurate nature of our scheme.

Example 3

Consider the nonlinear Convection-Reaction-Diffusion equation (Hundsdorfer, 2000): ut+aux=b2ux2+δu2(1-u),x[0,1],t0, with initial and boundary conditions u(x,0)=(1+exp(αx+γ))-1,u(0,t)=(1+exp(α(-βt)+γ))-1,u(1,t)=(1+exp(α(1-βt)+γ))-1.

The exact solution is given by u(x,t)=(1+exp(α(x-βt)+γ))-1 , where α=δ4b,β=2a+δb,γ=α(β-1) . The absolute errors in the solutions for different δ and appropriate parameter λ=-1.99 with b=0.1,h=k=0.01 , and t=0.9 are tabulated in Table 4, and compared with the results in Rashidinia and Shekarabi (2016), these results show that our presented method is more accurate.

Example 4

Consider the linear Convection-Reaction-Diffusion equation ut+aux=b2ux2,x[0,1],t0, with the following initial condition u(x,0)=exp-(x+0.5)20.00125 . The exact solution is given by u(x,t)=0.0250.000625+0.02texp-(x+0.5-t)20.00125+0.04t . The boundary conditions can be derived from the exact solution.

For this example, we put λ=-1.55,a=1 and b=0.01 . We take h=0.001 and k=0.0001 and the maximum absolute error in the solution for t=1 and t=2 are computed. The results are reported in Table 5 and compared with (Mittal and Jain, 2012), our numerical results these results show that our presented method is more accurate.

Example 5

Consider the linear Convection-Reaction-Diffusion equation ut=b2ux2-cu,x[0,1],t0, with initial and boundary conditions u(x,0)=Sin(nπx),u(0,t)=u(1,t)=0 . The exact solution is given by u(x,t)=exp((c-bπ2n2)t)Sin(nπx) .

For this example, we put λ=-2,b=0.1,c=-0.5 and n=1 . We take h=0.0125,h=0.025 and k=0.001,k=0.0001 and the maximum absolute error in the solution for t=0.8 are computed. The results are reported in Table 6 and compared with Biazar and Mehrlatifan (2018), Macias Diaz and Puri (2012), our numerical results these results show that our presented method is more accurate.

5

5 Conclusions

In this work, a new numerical method has been developed to the approximate solution of Convection-Reaction-Diffusion equation. Our method is based on the collocation method with extended cubic B-spline basis functions. The stability and convergence analysis of the method is described, we established unconditionally two level explicit finite difference scheme that it can be applied as a suitable scheme for modelling the behaviour of the similar problems. The applicability of our method has been considered by various examples. The numerical results show that our method provides more accurately than the recent existing methods. The value of an arbitrary λ is varied systemically, our scheme is unconditionally stable for λ-2 , the values of λ in our examples are different but they satisfied in this condition.

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