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Exact traveling wave solutions of the space–time fractional complex Ginzburg–Landau equation and the spacetime fractional Phi4 equation using reliable methods
Advances in Difference Equations volume 2019, Article number: 219 (2019)
Abstract
Ultrashort pulse propagation in optical transmission lines and phenomena in particle physics can be investigated via the cubic–quintic Ginzburg–Landau equation and the Phi4 equation, respectively. The main objective of this paper is to construct exact traveling wave solutions of the \((2 + 1)\)dimensional cubic–quintic Ginzburg–Landau equation and the Phi4 equation of spacetime fractional orders in the sense of the conformable fractional derivative. The method employed to solve the Ginzburg–Landau equation and the Phi4 equation are the modified Kudryashov method and the \((G'/G,1/G)\)expansion method, respectively. Several types of exact analytical solutions are obtained including reciprocal of exponential function solutions, hyperbolic function solutions, trigonometric function solutions and rational function solutions. Graphical representations and physical explanations of some of the obtained solutions are demonstrated using a range of fractional orders. All of the solutions have been verified by substitution into their corresponding equations with the aid of a symbolic software package. These methods are simple and efficient for solving the proposed equations.
1 Introduction
The investigation of exact solutions of nonlinear partial differential equations (NPDEs) plays an important role in study of physical phenomena in various scientific and engineering fields, such as biology, chemical kinetics, optical fiber, plasma physics and oceanic phenomena. Obtaining analytical and exact solutions of NPDEs for the above fields is important in analyzing the behaviors of the considered problems. Examples of recent developments in finding analytical and exact solutions for NPDEs are as follows. Guo and Lin used the ansatz method (e.g., a quadratic function or a linear combination of a quadratic and an exponential function) to obtain exact solutions of the \((2 + 1)\)dimensional Date–Jimbo–Kashiwara–Miwa (DJKM) equation [1]. Wazwaz and Kaur obtained optical solitons and singular soliton solutions of the selffocusing nonlinear Schrödinger (NLS) equation using the variational iteration method (VIM) [2]. Naghshband et al. analytically solved the generalized quintic complex Ginzburg–Landau equation using the homotopy analysis method (HAM) [3]. Seadawy employed the reductive perturbation method to construct solitary traveling wave solutions of the twodimensional nonlinear Kadomtsev–Petviashvili (KP) dynamic equation in dustacoustic plasmas [4] and the nonlinear threedimensional modified Zakharov–Kuznetsov (mZK) equation [5]. Mahmood and Yousif found novel analytical solutions for the modified Kawahara equation using the residual power series method [6]. Seadawy applied the auxiliary equation of the direct algebraic method to construct traveling wave solutions of the higherorder nonlinear Schrödinger equation [7]. In addition, the wellknown efficient methods for constructing exact solutions of NPDEs, which have been utilized in this research field, are the Expfunction method [8], the \((G'/G)\)expansion method [9], the first integral method [10], and the function transformation method [11].
In recent years, fractionalorder differential equations (FDEs) associated with fractional derivatives such as the Riemann–Liouville derivative [12], the Caputo derivative [12], the Caputo–Fabrizio derivative [13] and Jumarie’s modified Riemann–Liouville derivative [14] have been applied to numerous research areas such as applied mathematics, engineering, physics and finance. This is because the behavior of many systems shows after effects or memory which can be better explained using fractionalorder derivatives. Thus, FDEs are expansively used to model various complex phenomena. Many effective methods used to solve nonlinear differential equations of integer order are generalized to solve FDEs analytically and numerically such as the ADM [15], the VIM [16], the finite element method [17], and the predictorcorrector scheme or PECE (predictor, evaluate, corrector and evaluate) method [18]. In particular, the \((G'/G,1/G)\)expansion method [19,20,21,22], the modified Kudryashov method [23,24,25,26], the improved extended tanh–coth method [27] are used to get exact solutions of nonlinear fractional partial differential equations (NFPDEs).
In this paper, we are interested in using the modified Kudryashov method and the \((G'/G,1/G)\)expansion method to solve two partial differential equations arising in physics and engineering problems. Here a review of the modified Kudryashov method is briefly given as follows. Ege and Misirli [23] used the method to solve the spacetime fractional modified Benjamin–Bona–Mahony and potential Kadomtsev–Petviashvili equations. Zayed and Alurrfi [24] applied the modified Kudryashov method to seventhorder nonlinear partial differential equations including the Sawada–Kotera–Ito equation, the Kaup–Kupershmidt equation and the Lax equation. Hosseini et al. [25] employed the method to solve the conformable timefractional Klein–Gordon equations with quadratic and cubic nonlinear terms. The fractional generalized reaction Duffing model equation, the fractional biological population model and the fractional diffusion reaction equation were solved via the modified Kudryashov method [26]. For the \((G'/G,1/G)\)expansion method, Muhammad and Syed [19] applied the method to obtain exact solutions of the positive GardnerKP equation. Demiray et al. [20] used the \((G'/G,1/G)\)expansion method to solve the new Hamiltonian amplitude equation and the Broer–Kaup equation. Zayed and Alurrfi [21] employed this method to solve two nonlinear Schrödinger equations. The method was used to find exact solutions of the \((3 + 1)\)dimensional spacetime fractional Jimbo–Miwa equation by Sirisubtawee et al. [22].
We will apply the two methods mentioned above to construct exact solutions for the following two conformable spacetime fractional order partial differential equations. The first one is the fractional \((2 + 1)\)dimensional cubic–quintic Ginzburg–Landau equation which will be solved using the modified Kudryashov method. The second problem is the nonlinear fractional Phi4 equation for which the \((G'/G,1/G)\)expansion method will be used. Some recent work utilizing the conformable fractional derivative in real world problems such the Burgers–KdV equation, the KdV–Zakharov–Kuznetsev equation, the unstable Schrödinger equation, and the resonant nonlinear Schrödinger equation have been studied in [28,29,30]. In addition, exact solutions to equations associated with the above two problems have been found using many methods. Some examples are as follows. For the \((2 + 1)\)dimensional nonlinear cubic–quintic Ginzburg–Landau equation, Shi et al. [31] used a novel identical rewriting of the differential equation method and the Expfunction method to construct solitary solutions and periodic solutions of the equation. Zayed and Alurrfi [21] obtained traveling wave solutions using the \((G'/G,1/G)\)expansion method. The new extended auxiliary equation method was applied to construct many new types of Jacobi elliptic function solutions for the equation by Zayed and Alurrfi [32]. The new mapping method was employed for finding many other new exact solutions of the equation by Zayed and AlNowehy [33] and they concluded that this method and the extended auxiliary equation method are efficient techniques for finding exact solutions of NPDEs in mathematical physics. For the Phi4 equation, Akter and Akbar [34] implemented the modified simple equation (MSE) method to find a solitary wave solution of the equation. Tariq and Akram [35] utilized the tanh method along with the fractional complex transform to solve the time fractional Phi4 equation. Khan et al. [36] applied the \((G'/G)\)expansion method to attain new solitary wave solutions of the spacetime fractional Phi4 equation in the sense of the modified Riemann–Liouville fractional operator. Akram [37] used the modified Kudryashov method and the \(\exp ( \varPhi (\xi ))\) method to extract the exact solutions of the nonlinear fractional Phi4 equation in the sense of the conformable timefractional derivative.
Here the spacetime fractional \((2 + 1)\)dimensional cubic–quintic Ginzburg–Landau equation and nonlinear fractional Phi4 equation in the sense of the conformable fractional derivative, for which we wish to obtain exact solutions, are as follows.

1.
The spacetime fractional \((2 + 1)\)dimensional cubic–quintic Ginzburg–Landau equation [33] is written as
$$ \begin{aligned}[b] &iD^{\delta }_{z} u+\frac{1}{2}D^{2\beta }_{x} u+\frac{1}{2}(\beta _{1}i)D ^{2\alpha }_{\tau }u+iu+(1ir_{1})u \rvert u \rvert ^{2}+ir_{2}u \rvert u \rvert ^{4} =0,\\ & \quad 0< \delta ,\beta ,\alpha \leq 1, \end{aligned} $$(1)where \(D^{\eta }_{s} u\) is the conformable fractional derivative of u with respect to s of order η. The equation describes the propagation of optical pulses in optic fibers in which the complex function \(u=u(x, z, \tau )\) is a slowly varying envelop of the electric field, the parameters \(\beta _{1}<0\), \(r_{1}\) and \(r_{2}\) are real constant, and the variables z and x are the propagation and transverse coordinates, respectively. The variable \(\tau =t\frac{z}{V _{0}}\) is the socalled reduced time, where t is the physical time, and \(V_{0}\) is the group velocity of the carrier wave.

2.
The conformable spacetime fractional Phi4 equation is expressed as [36]
$$ D_{t}^{2\alpha }uD_{x}^{2\beta }u+m^{2}u+nu^{3}=0, \quad 0< \alpha ,\beta \leq 1, $$(2)where \(D_{s}^{\eta }u\) denotes the conformable fractional derivative of u with respect to s of order η and m, n are real constants. The equation has played an important role in particle and nuclear physics.
The rest of this paper is organized as follows. In Sect. 2, the definition of the conformable fractional derivative and some of its important properties are given. In Sect. 3, we provide the main steps of the modified Kudryashov method and the \((G'/G,1/G)\)expansion method. The applications of the two methods to the mentioned fractionalorder problems are presented in Sect. 4. In Sect. 5, graphs and physical explanations of some selected exact solutions of the two equations are described. Some conclusions and discussions are given in Sect. 6.
2 The conformable fractional derivative and its properties
In this section, the definition of the conformable fractional derivative and its vital properties are given as follows.
Definition 1
Given a function \(f:[0,\infty )\rightarrow \mathbb{R}\). Then the conformable fractional derivative of f of order α is defined by [26, 38]
If the limit in Eq. (3) exists, then we say that f is αconformable differentiable at a point \(t>0\).
Theorem 1
Let \(\alpha \in (0,1]\), and \(f(t)\), \(g(t)\) be αconformable differentiable at a point \(t>0\), then
Remark 1
Conformable fractional derivatives of some important functions are as follows [38].

(1)
\(D_{t}^{\alpha }(e^{ct})=ct^{1\alpha }e^{ct}\), \(c \in \mathbb{R}\).

(2)
\(D_{t}^{\alpha }(\sin bt)=bt^{1\alpha }\cos bt\), \(b \in \mathbb{R}\).

(3)
\(D_{t}^{\alpha }(\cos bt)=bt^{1\alpha }\sin bt\), \(b \in \mathbb{R}\).

(4)
\(D_{t}^{\alpha }(\frac{1}{\alpha }t^{\alpha })=1\).

(5)
\(D_{t}^{\alpha }(f(t))=t^{1\alpha }\frac{df(t)}{dt}\), provided that \(f(t)\) is differentiable.
Theorem 2
Let \(f:(0,\infty )\rightarrow \mathbb{R} \) be a function such that f is differentiable and αconformable differentiable. Also, let g be a differentiable function defined in the range of f. Then
where the prime notation (′) denotes the classical derivative.
3 Methods
Consider a nonlinear fractional evolution partial differential equation in three independent variables t, x, and y as follows:
where \(D_{t}^{\alpha }u\), \(D_{x}^{\beta }u\), and \(D_{y}^{\gamma }u\) are the conformable derivatives of a dependent variable u with respect to independent variables t, x, and y. F is a polynomial of the unknown function \(u=u(x,y,t)\) and its various partial derivatives in which the highestorder derivatives and nonlinear terms are associated. Using the following traveling wave transformation:
where k, l, and c are constants to be determined later, Eq. (4) is reduced to an ODE in \(u=u(\xi )\),
where P is a polynomial of \(u(\xi )\) and its various derivatives and the prime notation (′) denotes the derivative with respect to ξ.
3.1 The modified Kudryashov method
The main steps of the modified Kudryashov method are as follows [23,24,25,26].
Step 1. We assume that the exact solutions of Eq. (6) can be expressed in the following form:
where the coefficients \(a_{i}\) (\(i=0,1,\ldots, N1\)) and \(a_{N}\neq 0\) are constants to be determined later and the function Q is of the form
\(Q(\xi )\) satisfies the following differential equation:
where \(a>0\), \(a\neq 1\). If \(a=e\), then the method reduces to the Kudryashov method which has been proposed by many authors [39,40,41].
Step 2. The value of the positive integer N in Eq. (7) can be computed by balancing the highestorder nonlinear term with the highestorder derivative in \(u(\xi )\) occurring in Eq. (6). If the degree of \(u(\xi )\) is \(\operatorname{Deg}[u(\xi )]= N\), then the degree of the other terms can be expressed as
Remark 2
In some nonlinear equations, if the balance number N is not a positive integer (e.g., a fraction or a negative integer), then a special transformation is required. The approaches to setting such a transformation can be found in [21, 42].
Step 3. We substitute the result of Eq. (7) into Eq. (6) with the aid of Eq. (9), then we obtain polynomials in \(Q(\xi )\). Collecting all coefficients of like power (i.e., \(Q(\xi )^{i}\), \(i=0,1,2,\ldots ,M\), where M is some positive integer) of the resulting polynomials and setting them to zero, we obtain a system of algebraic equations which can be solved using a symbolic software package to get the unknowns \(a_{i}\) (\(i=0,1,\ldots ,N\)), k, l, and c.
Step 4. We substitute the obtained unknown values from Step. 3 together with the function \(Q(\xi )\) in Eq. (8) into Eq. (7) to get the exact solutions of Eq. (4) with ξ in Eq. (5).
3.2 The \((G'/G,1/G)\)expansion method
Before we give the main steps of the \((G'/G,1/G)\)expansion method, it is necessary to introduce the following concept [19,20,21,22]. Consider the following secondorder linear ODE:
where the prime notation (′) denotes the derivative with respect to ξ and where λ, μ are constants. We then set the functions ϕ and ψ as follows:
Equations (11) and (12) can be converted into the following system of two nonlinear ordinary differential equations:
The solutions of Eq. (11) can be categorized into the following three cases.
Case 1: If \(\lambda <0\), then the general solution of (11) is of the form
and we have
where \(A_{1}\) and \(A_{2}\) are arbitrary constants and \(\sigma _{1}=A _{1}^{2}A_{2}^{2}\).
Case 2: If \(\lambda >0\), then the general solution of (11) can be given as
and we have the following associated relation:
where \(A_{1}\) and \(A_{2}\) are arbitrary constants and \(\sigma _{2}=A _{1}^{2}+A_{2}^{2}\).
Case 3: If \(\lambda =0\), then the general solution of (11) can be written as
and the corresponding relation is
where \(A_{1}\) and \(A_{2}\) are arbitrary constants.
The main steps of the \((G'/G,1/G)\)expansion method [19,20,21,22] are as follows.
Step 1. Suppose that the solution to Eq. (6) can be expressed in terms of a polynomial of the two variables ϕ and ψ as
where \(a_{0}\), \(a_{j}\), and \(b_{j}\) (\(j=1,2,\ldots ,N\)) are constants to be determined later with \(a_{N}^{2}+b_{N}^{2}\neq 0\) and where the functions \(\phi =\phi (\xi )\) and \(\psi =\psi (\xi )\) are implicitly related to Eq. (11) via the relations in Eq. (12).
Step 2. We find the value of the positive integer N which can be computed by balancing the highestorder derivative and the nonlinear terms in Eq. (6). Suppose that the degree of \(u(\xi )\) is \(\operatorname{Deg}[u( \xi )]= N\), then the degree of other terms will be given by Eq. (10).
Step 3. Substituting the result from Eq. (20) into Eq. (6) with the aid of Eq. (13) and Eq. (15), the function P in Eq. (6) can be converted into a polynomial in ϕ and ψ, in which the degree of ψ will be one. Equating each coefficient of the resulting polynomial to zero, we obtain a system of algebraic equations, which can be solved using a symbolic computational package, for the unknowns \(a_{0},a_{j},b_{j}\) (\(j=1,2,\ldots ,N\)), k, l, c, μ, λ (<0), \(A_{1}\), and \(A_{2}\). Hence, the exact solutions of Eq. (4) generated by this step with the transformation in Eq. (5) are obtained in terms of hyperbolic functions.
Step 4. In the same manner as Step 3, substituting the result from Eq. (20) into Eq. (6) with the aid of Eq. (13) and Eq. (17) for \(\lambda >0\), we can obtain the exact solutions of Eq. (4) by using the transformation in Eq. (5). The obtained exact solutions in this step are in terms of trigonometric functions.
Step 5. Similar to Step 3, substituting the result from Eq. (20) into Eq. (6) with the aid of Eq. (13) and Eq. (19) for \(\lambda =0\), we can get the traveling wave solutions of Eq. (4) with the aid of the transformation in Eq. (5). The resulting exact solutions in this step are obtained in terms of rational functions.
4 Exact solutions to NFPDEs
In this section, we will apply the modified Kudryashov method to find the exact traveling wave solutions of the spacetime fractional \((2 + 1)\)dimensional cubic–quintic Ginzburg–Landau equation as given by Eq. (1) and use the \((G'/G,1/G)\)expansion method to obtain exact solutions of the conformable spacetime fractional Phi4 equation as given by Eq. (2).
4.1 Obtaining exact solutions of Eq. (1) using the modified Kudryashov method
In order to solve Eq. (1), we assume that the exact solution has the following form:
where \(w(x,\tau )\) and \(\varphi (x,\tau )\) are realvalued functions of x and τ. The parameter k is a real constant and the parameter δ is as defined in Eq. (1). Substituting Eq. (21) into Eq. (1) and then separating the real and imaginary parts of the resulting equation, we obtain the following equations:
where the notation \(D_{\gamma }^{\kappa }v\) is the conformable fractional derivative of order κ of v with respect to γ.
Let
The parameters \(p_{0}\), \(p_{1}\), \(q_{0}\) and \(q_{1}\) in Eq. (24) are real constants to be determined later. We substitute Eq. (24) into Eqs. (22) and (23) to obtain
where the prime notation (′) of w and φ denotes the derivative of w and φ with respect to ξ and η, respectively.
Setting \(q_{1}=\frac{q_{0}}{\sqrt{\beta _{1}}}\), \(p_{1}=\frac{p_{0}}{\sqrt{ \beta _{1}}}\), and then mathematically manipulating them, we have the following relations:
Using Eq. (27), Eqs. (25) and (26) can be reduced to
Let \(\varphi (\eta )= \eta \) where η is given in Eq. (24), then
Using Eq. (30), Eq. (28) is reduced to
From Eq. (31), we obtain
Using Eq. (30), Eq. (29) can be written as
Comparing the coefficients of Eqs. (32) and (33), we get the following relations:
Simplifying Eq. (34), we obtain
where the parameters \(r_{1}\) and \(r_{2}\) must satisfy the relation \(3r_{1}^{2}=16r_{2}+12\).
Substituting the above expressions for k and \(q_{1}\) into Eq. (32) (or (33)), we attain an ODE as follows:
We multiply both sides of Eq. (36) by \(w'\) and then integrate the resulting equation with respective to ξ to obtain
where \(k_{0}\) is a constant of integration. Using Eq. (10) to balance the terms \((w')^{2}\) and \(w^{6}\) in Eq. (37), we get \(N=\frac{1}{2}\). According to Remark 2 in Sect. 3, we let \(v(\xi )\) be a new function satisfying the following transformation:
Putting Eq. (38) into Eq. (37), we get the following ODE in the variable v:
Again using Eq. (10) to balance the terms \((v')^{2}\) and \(v^{4}\) in Eq. (39), we obtain \(N=1\). Therefore, the solution form of Eq. (39) is
where \(a_{0}\), \(a_{1}\) (≠0) are constants to be determined later. Substituting Eq. (40) along with Eq. (9) into Eq. (39) and equating all the coefficients of like power of \(Q(\xi )\) to be zero, we find the following algebraic system:
Solving system (41) with the aid of the Maple package program, we obtain the following cases.
Case 1:
where \(r_{2}>0\).
Using Eqs. (8), (21), (24), (38), (40), and (42), we have the exact solution of Eq. (1) as follows:
where \(\xi =\pm \frac{\sqrt{\frac{6\beta _{1}}{r_{2}}} r_{1}}{2 \beta \ln a }x^{\beta }\mp \frac{\sqrt{\frac{6}{r_{2}}} r_{1}}{2 \alpha \ln a }\tau ^{\alpha }\).
Case 2:
where \(r_{2}>0\).
Using Eqs. (8), (21), (24), (38), (40), and (44), we get the traveling wave solution of Eq. (1) as follows:
where \(\xi =\pm \frac{\sqrt{\frac{6\beta _{1}}{r_{2}}} r_{1}}{2 \beta \ln a }x^{\beta }\mp \frac{\sqrt{\frac{6}{r_{2}}} r_{1}}{2 \alpha \ln a }\tau ^{\alpha }\).
4.2 Obtaining exact solutions of Eq. (2) using the \((G'/G,1/G)\)expansion method
We apply the traveling wave transformation
where k and c are arbitrary constants. Using Theorem 2 and the above transformation, the conformable fractionalorder derivatives of u in Eq. (2) become
Hence, Eq. (2) is reduced to the following ODE in the variable \(u=u(\xi )\):
where the prime notation (′) denotes the derivative with respect to ξ.
Applying the formulas in Eq. (10) to balance the highestorder derivative and nonlinear terms, i.e., \(u''\) and \(u^{3}\) in Eq. (47), we obtain \(N=1\). Hence the solution form of Eq. (47) is
where the constant coefficients \(a_{0}\), \(a_{1}\), and \(b_{1}\) are to be determined later, subject to the inequality \(a_{1}^{2}+b_{1}^{2} \neq 0\). There are three cases of the function \(G(\xi )\) associated with the functions \(\phi (\xi )\) and \(\psi (\xi )\) of the solution in Eq. (48) depending on the sign of λ, as described in Sect. 3.
Case 1 (Hyperbolic function solutions): If \(\lambda <0\), we substitute Eq. (48) into Eq. (47) and utilize Eqs. (13) and (15) so that the lefthand side of Eq. (47) becomes a polynomial in \(\phi (\xi )\) and \(\psi (\xi )\). Setting all of the coefficients of this resulting polynomial to be zero, we obtain the following system of nonlinear algebraic equations in \(a_{0}\), \(a_{1}\), \(b_{1}\), k, c, μ and λ:
Solving the above algebraic system using the Maple package program, we get the following results.
Result 1
where \(c^{2}>k^{2}\), \(n<0\) and m is an arbitrary constant.
From Eqs. (14), (48), and (50), we obtain the exact solution of Eq. (2) as follows:
where ξ is defined in Eq. (46).
Result 2
where \(c^{2}< k^{2}\), \(n\sigma _{1}>0\) and m is an arbitrary constant.
From Eqs. (14), (48), and (52), we have the exact solution of Eq. (2) as follows:
where ξ is defined in Eq. (46) and \(\sigma _{1}=A _{1}^{2}A_{2}^{2} \neq 0\).
Result 3
where \(c^{2}>k^{2}\), \(n<0\), \(\sigma _{1}>0\) and m is an arbitrary constant.
From Eqs. (14), (48), and (54), we deduce the traveling wave solution of Eq. (2) as follows:
where ξ is defined in Eq. (46) and \(\sigma _{1}=A _{1}^{2}A_{2}^{2}\).
Result 4
where \(c^{2}\geq 2k^{2}\), \(n<0\), \(m\neq 0\), \(\sigma _{1}\geq 0\) and μ is an arbitrary constant.
From Eqs. (14), (48), and (56), we obtain the exact solution of Eq. (2) as follows:
where ξ is defined in Eq. (46) and \(\sigma _{1}=A _{1}^{2}A_{2}^{2}\).
Case 2 (Trigonometric function solutions): If \(\lambda >0\), we substitute Eq. (48) into Eq. (47) and utilize Eqs. (13) and (17) so that the lefthand side of Eq. (47) becomes a polynomial in \(\phi (\xi )\) and \(\psi (\xi )\). Setting all of the coefficients of the resulting polynomial to be zero, we get the system of nonlinear algebraic equations in \(a_{0}\), \(a_{1}\), \(b_{1}\), k, c, μ and λ as follows:
By solving the above algebraic system using the Maple package program, we obtain the following results.
Result 1
where \(c^{2}< k^{2}\), \(n>0\) and m is an arbitrary constant.
From Eqs. (16), (48), and (59), we obtain the traveling wave solution of Eq. (2) as follows:
where ξ is defined in Eq. (46).
Result 2
where \(c^{2}>k^{2}\), \(n<0\) and m is an arbitrary constant.
From Eqs. (16), (48), and (61), we get the exact solutions of Eq. (2) as follows:
where ξ is defined in Eq. (46) and \(\sigma _{2}=A _{1}^{2}+A_{2}^{2}\).
Result 3
where \(c^{2}< k^{2}\), \(n>0\) and m is an arbitrary constant.
From Eqs. (16), (48), and (63), we have the exact solution of Eq. (2) as follows:
where ξ is defined in Eq. (46) and \(\sigma _{2}=A _{1}^{2}+A_{2}^{2}\).
Result 4
where \(c^{2}< k^{2}\), \(n>0\), \(m\neq 0\) and μ is an arbitrary constant.
From Eqs. (16), (48), and (65), we obtain the exact solution of Eq. (2) as follows:
where ξ is defined in Eq. (46) and \(\sigma _{2}=A _{1}^{2}+A_{2}^{2}\).
Case 3 (Rational function solutions): If \(\lambda =0\), we substitute Eq. (48) into Eq. (47) and utilize Eqs. (13) and (19) so that lefthand side of Eq. (47) turns out to be a polynomial in \(\phi (\xi )\) and \(\psi (\xi )\). Setting all of the coefficients of this resulting polynomial to zero, we obtain the system of nonlinear algebraic equations in \(a_{0}\), \(a_{1}\), \(b_{1}\), k, c and μ as follows:
Using the Maple package program to solve the above algebraic system, we obtain the following results.
Result 1
where \(n(c^{2}k^{2})<0\) and \(A_{1}\neq 0\).
From Eqs. (18), (48), and (68), we get the exact solutions of Eq. (2) as follows:
where ξ is defined in Eq. (46) and \(A_{2}\) is an arbitrary constant.
Result 2
where \(n(c^{2}k^{2})<0\), \(n(2c^{2}\mu A_{2}c^{2}A_{1}^{2}2k^{2} \mu A_{2}+k^{2}A_{1}^{2})>0\) and μ is an arbitrary constant.
From Eqs. (18), (48), and (70), we attain the traveling wave solution of Eq. (2) as follows:
where ξ is defined in Eq. (46).
5 Graphical representations and their physical explanations for selected solutions
In this section, we will provide some graphical representations of the exact solutions of the spacetime fractional \((2 + 1)\)dimensional cubic–quintic Ginzburg–Landau equation as in Eq. (1) and the spacetime fractional Phi4 equation as in Eq. (2). Additionally, we will also discuss their physical explanations. The selected exact explicit solutions of Eq. (1) are plotted on \(10\leq x\leq 10\) and \(5\leq \tau \leq 5\) while the variable z is temporarily ignored, i.e., \(z=0\). The selected solutions of Eq. (2) are portrayed on \(10\leq x\leq 10\) and \(5\leq t \leq 5\). The fractional orders α, β of both equations are varied among 1, 0.9 and 0.8. The graphical results of the selected solutions of each problem are described below.
The fixed values \(r_{1}=2\sqrt{5}\), \(r_{2}=3\), \(\beta _{1}=1\), \(d=1\), \(a=2\) and the variation of α, \(\beta \in \{1, 0.9, 0.8\}\) are used to plot the real part of the exact solution \(u_{2}(x,z,\tau )\) in Eq. (45) of Eq. (1), which is constructed using the modified Kudryashov method. The graphs of its real part are shown in Fig. 1. They represent the oscillatory wave solutions.
Graphical representations are portrayed below using the selected exact solutions of Eq. (2) constructed from the \((G'/G,1/G)\)expansion method. Using the fixed values \(m = 2\), \(n = 3\), \(k = 1\), \(c = 9\), \(A_{1} = 1\), and \(A_{2} = 3\), the exact solutions \(u_{1}(x,t)\) in Eq. (51) corresponding to the variation of α, β are plotted in Fig. 2 as follows. The solution \(u_{1}(x,t)\) with \(\alpha =\beta =1\) describing the kinkshaped soliton solution is depicted in Fig. 2(a). The graphs of the solution \(u_{1}(x,t)\) with \(\alpha =\beta =0.9 \) and \(\alpha =0.9\), \(\beta =0.8\), demonstrating the discontinuous kinkshaped soliton solutions, are presented in Figs. 2(b) and (c), respectively. The graph of \(u_{1}(x,t)\) with \(\alpha =0.9\), \(\beta =0.8\) is shown in Fig. 2(d).
For the fixed values \(m = 2\), \(n = 3\), \(k = 9\), \(c = 1\), \(A_{1} = 1\), and \(A_{2} = 3\), the exact solutions \(u_{2}(x,t)\) in Eq. (53) of Eq. (2) corresponding to the variation of α, \(\beta \in \{1, 0.9, 0.8\}\) are scrutinized. The solution \(u_{2}(x,t)\) with \(\alpha =\beta =1\) describing the antisoliton solution is plotted in Fig. 3(a). The graphs of the solution \(u_{2}(x,t)\) with \(\alpha =\beta =0.9 \) and \(\alpha =0.9\), \(\beta =0.8\) indicating the discontinuous the antisoliton solution are presented in Figs. 3(b) and (c), respectively. The graph of \(u_{2}(x,t)\) with \(\alpha =0.9\), \(\beta =0.8\) is plotted in Fig. 3(d).
In Fig. 4(a), we have presented the singular kinkshaped soliton solutions obtained from the solution \(u_{3}(x,t)\) in Eq. (55) when the parameter values \(m = 1\), \(n = 3\), \(k = 1\), \(c = 9\), \(A_{1} = 3\), and \(A_{2} = 1\) and the fractional orders \(\alpha =\beta =1\) are used. Using the same parameter values as above but \(\alpha =\beta =0.9\) and \(\alpha =0.9\), \(\beta =0.8\), the singular singlesoliton solution and the singular multiplesoliton solution for \(u_{3}(x,t)\) in Eq. (55) are plotted in Figs. 4(b) and (c), respectively. We can see that their graphs are not plotted on the entire domain since these solutions are real only on a certain part of the domain. The graph of \(u_{3}(x,t)\) with \(\alpha =0.9\), \(\beta =0.8\) is shown in Fig. 4(d).
For the fixed values \(m = 2\), \(n = 3\), \(k = 9\), \(c = 1\), \(A_{1} = 1\), and \(A_{2} = 3\), the graphs of the exact solutions \(u_{2}(x,t)\) in Eq. (62) of Eq. (2) corresponding to the variation of α, β are investigated. The solution \(u_{2}(x,t)\) with \(\alpha =\beta =1\) describing the singular multiplesoliton solution is depicted in Fig. 5(a). The solutions \(u_{2}(x,t)\) with \(\alpha =\beta =0.9 \) and \(\alpha =0.9\), \(\beta =0.8\) describing the singular multiplesoliton solution are presented in Figs. 5(b) and (c), respectively. The graph of \(u_{2}(x,t)\) with \(\alpha =0.9\), \(\beta =0.8\) is plotted in Fig. 5(d).
For the fixed values \(m = 2\), \(n = 3\), \(k = 9\), \(c = 1\), \(A_{1} = 1\), and \(A_{2} = 3\), the graphs of the exact solution \(u_{1}(x,t)\) in Eq. (69) of Eq. (2) corresponding to the variation of α, β are displayed. The solution \(u_{2}(x,t)\) with \(\alpha =\beta =1\) describing the kinkshaped soliton solutions is depicted in Fig. 6(a). The solutions \(u_{1}(x,t)\) with \(\alpha =\beta =0.9 \) and \(\alpha =0.9\), \(\beta =0.8\), showing the singular singlesoliton solution, are presented in Figs. 6(b) and (c), respectively. The graph of \(u_{1}(x,t)\) with \(\alpha =0.9\), \(\beta =0.8\) is shown in Fig. 6(d).
6 Conclusions
In this article, we have determined many explicit exact solutions of the nonlinear conformable spacetime fractional complex Ginzburg–Landau equation as given by Eq. (1) using the modified Kudryashov method and of the conformable spacetime fractional Phi4 equation as given by Eq. (2) using the \((G'/G,1/G)\)expansion method. Some of the obtained solutions are distinct from those found previously via different methods. The fractional complex transform and the symbolic computation package Maple 17 have been used to assist the methods for obtaining the exact solutions of the problems. The exact solutions of Eq. (1) obtained by the modified Kudryashov method are the product of the reciprocal of an exponential function and the exponential function of a purely imaginary function. For Eq. (2), many exact solutions, including hyperbolic function solutions, trigonometric function solutions and rational function solutions, are constructed using the \((G'/G,1/G)\)expansion method. Some of these exact solutions have been graphically characterized in terms of a variety of distinct physical structures such as an oscillatory wave solution, a kinkshaped soliton solution, a singular singlesoliton solution, a singular multiplesoliton solution and an antisoliton solution. Some of our obtained exact solutions are similar to the solutions in [36] which was solved using the \((G'/G)\)expansion method. However, our solutions are the generalization of their solutions because the \((G'/G,1/G)\)expansion method can be reduced to the \((G'/G)\)expansion method by setting the parameter μ in Eq. (11) and the coefficient \(b_{j}\) in Eq. (20) to be zero. Therefore, the \((G'/G,1/G)\)expansion method is an extension of the \((G'/G)\)expansion method. The applications of these solutions have been found in many physical phenomena such as optical fibers and nuclear physics. All of our results obtained by the two methods have been attained and verified by substituting them back into the original problems with the aid of the Maple 17 package program. Since the two methods are powerful, systematic and reliable for obtaining the exact solutions of the equations, they could be applied efficiently for a great many NPDEs including fractionalorder ones arising in mathematical physics.
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The authors would like to express their sincere thanks to the anonymous referees for their time and valuable comments.
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This research was funded by King Mongkut’s University of Technology North Bangkok under contract no. KMUTNB61KNOW037.
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Sirisubtawee, S., Koonprasert, S., Sungnul, S. et al. Exact traveling wave solutions of the space–time fractional complex Ginzburg–Landau equation and the spacetime fractional Phi4 equation using reliable methods. Adv Differ Equ 2019, 219 (2019). https://doi.org/10.1186/s1366201921549
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DOI: https://doi.org/10.1186/s1366201921549