Research Article | Open Access

Yongyi Gu, Fanning Meng, "Searching for Analytical Solutions of the (2+1)-Dimensional KP Equation by Two Different Systematic Methods", *Complexity*, vol. 2019, Article ID 9314693, 11 pages, 2019. https://doi.org/10.1155/2019/9314693

# Searching for Analytical Solutions of the (2+1)-Dimensional KP Equation by Two Different Systematic Methods

**Academic Editor:**Irene Otero-Muras

#### Abstract

In this paper, we derive analytical solutions of the (2+1)-dimensional Kadomtsev-Petviashvili (KP) equation by two different systematic methods. Using the -expansion method, exact solutions of the mentioned equation including hyperbolic, exponential, trigonometric, and rational function solutions have been obtained. Based on the work of Yuan* et al.*, we proposed the extended complex method to seek exact solutions of the (2+1)-dimensional KP equation. The results demonstrate that the applied methods are efficient and direct methods to solve the complex nonlinear systems.

#### 1. Introduction

The (2+1)-dimensional KP equation [1] is given bywhich is a universal nonlinear integrable system in two spatial and one temporal coordinates and can be utilized to describe the law of motion of water waves in (2+1)-dimensional spaces and plasmas in magnetic fields [2–4]. For example, in the study of water waves, this equation appears in the description of a tsunami wave travelling in the inhomogeneous zone on the bottom of the ocean [2], and it also appears in the study of nonlinear ion acoustic waves in magnetized dusty plasma [4]. Over the past few years, many research results for the (2+1)-dimensional KP equation have been generated. As to this equation, traveling wave solutions [5, 6], rogue wave, and a pair of resonance stripe solitons [7] are discovered. Symmetry reductions [8] and conservation laws [9] are also investigated. Using the Hirota bilinear form of the (2+1)-dimensional KP equation, mixed lump-kink solutions are presented under the help of Maple [10]. By the positive quadratic function and exponential function, rational lump solutions and line soliton pairs to the (2+1)-dimensional KP equation are established [11].

It is well known that nonlinear differential equations (NLDEs) are universally applied in plasma physics, solid state physics, nonlinear optics, fluid dynamics, biology, chemistry, etc. For instance, the singular behaviors [12, 13] and impulsive phenomena [14, 15] often show some blow-up properties [16, 17] which happen in lots of complex physical processes. In order to solve various differential equations, some analytical tools as well as symbolic calculation techniques were established, such as fixed-point theorems [18, 19], variational methods [20, 21], topological degree method [22–25], iterative techniques [26, 27], bilinear method [28–31], modified simple equation method [32], -expansion method [33–38], Lie group method [39, 40], and complex method [41–50].

The -expansion method is an efficient method for finding the exact solutions of NLDEs. Many researchers, such as Roshid, Khan, and Jafari, have used this method to study NLDEs [35–37]. The complex method, proposed by Yuan* et al.* [41, 42], is established via complex differential equations and complex analysis. It is a useful tool to find exact solutions of NLDEs which are Briot-Bouquet equations or satisfy condition [41]. Based on the work of Yuan* et al.*, we introduce the extended complex method to seek exact solutions of NLDEs which are not Briot-Bouquet equations or do not satisfy condition. The extended complex method can solve more differential equations in mathematical physics than the complex method. In this paper, two different systematic methods which are the -expansion method and extended complex method are employed to search analytical solutions of the (2+1)-dimensional KP equation. Computer simulations are given to illustrate our main results. Comparisons and conclusions are presented in the last section.

#### 2. The -Expansion Method

Consider a nonlinear PDE as follows:where is a polynomial consisting of the unknown function , the partial derivatives of , the highest-order partial derivatives of , and some nonlinear terms.

*Step 1. *Substitute traveling wave transformation,into (2) to convert it to the ODE,where is a polynomial of and its derivatives.

*Step 2. *Suppose that (4) has the following exact solutions:where are constants to be determined later, such that and satisfies the ODE as follows:Equation (6) has the solutions as follows.

When , ,When , ,When , , ,When , , ,When , , , where is an arbitrary constant and are constants in (7)- (13). We determine the positive integer through considering the homogeneous balance between the highest-order derivatives and nonlinear terms of (4).

*Step 3. *Inserting (5) into (4) and then considering the function yields a polynomial of . Let the coefficients of the same power about equal zero; then, we get a set of algebraic equations. We solve the algebraic equations to obtain the values of and then we put these values into (5) along with (7)-(13) to finish the determination of the solutions for the given PDE.

#### 3. Application of the -Expansion Method to the (2+1)-Dimensional KP Equation

Substituteinto (1), and we get

Take the homogeneous balance between and in (15) to yieldwhere and and are constants.

Substituting into (15) and equating the coefficients about to zero, we get

Solving the above algebraic equations yieldswhere and are arbitrary constants.

We substitute (18) into (16), and thenUsing (7) to (13) into (19), respectively, we obtain exact solutions of the (2+1)-dimensional KP equation as follows.

When , ,

When , ,When , , ,When , , ,When , , ,The properties of the solutions are shown in Figures 1–5.

*Remark*. The -expansion method is an efficient method. Khan and Akbar [6] used this method to obtain the exact solutions of the KP equation. We still give the details of solving KP equation with the -expansion method in this paper for several reasons. First of all, we consider fourth-order ODE after the reduction instead of the second-order ODE of [6], so it is also a good example to show the use of the -expansion method. Secondly, we obtain more generalized results compared with [6]. If we take , , and , then the results of [6] can be obtained. Thirdly, we give some computer simulations to show the properties of the solutions.

#### 4. The Extended Complex Method

*Step 1. *Substituting the transform , into the given PDE yields

*Step 2. *Determine the weak condition.

Let , and suppose that the meromorphic solutions of (25) have at least one pole. Substituting the Laurent series,into (25), if it is determined distinct Laurent singular partsthen the weak condition of (25) holds.

Weierstrass elliptic function with double periods satisfies the equation as follows:and has the following addition formula [51]:

*Step 3. *Substitute the indeterminate formsinto (25), respectively, to yield the systems of algebraic equations, and solve the algebraic equations to obtain elliptic function solutions, rational function solutions, and simply periodic solutions with the pole at , where are determined by (26), and , and , have distinct poles of multiplicity .

*Step 4. *Obtain the meromorphic solutions with arbitrary pole, and substitute the inverse transform into the meromorphic solutions to achieve the exact solutions to the original PDE.

#### 5. Application of the Extended Complex Method to the (2+1)-Dimensional KP Equation

Inserting (26) into (15) yields , and then the weak condition of (15) holds.

By the weak condition and (30), we have the form of the elliptic solutions of (15):with pole at .

Inserting into (15), we havewhere

Equating the coefficients of all powers about in (34) to zero, we get a system of algebraic equations:

Solving the above equations, we obtainand then

Therefore, the elliptic solutions of (15) with arbitrary pole arewhere .

Apply the addition formula to , and thenwhere and and are arbitrary constants.

By the weak condition and (31), we have the indeterminate forms of rational solutions:with pole at .

Inserting into (15), we havewhere

Equating the coefficients of all powers about in (42) to zero, we get a system of algebraic equations:

Solving the above equations, we obtainand then

Substitute into (15), and thenwhere ().

Substitutinginto (47), we obtain thatwhere

Equating the coefficients of all powers about in (49) to zero, we get a system of algebraic equations:

Solving the above equations, we obtain

Therefore, simply periodic solutions to (15) with pole at are

Similar to , we substituteinto (47) to yieldand then

Substitutinginto (47) to yieldthen

By the above procedures, we collect meromorphic solutions of (15) with arbitrary pole as follows:where and and are arbitrary constants.

The properties of the solutions are shown in Figures 6–8.

*Remark*. Based on the work of Yuan* et al.* [41, 42], we put forward the extended complex method for the first time. To our knowledge, the solutions obtained by this method have not been reported in former literature.

#### 6. Comparisons and Conclusions

Borhanifar* et al.* [5] utilized the sine-cosine, the standard tanh, and the extended tanh methods to study the (2+1)-dimensional KP equation. We can observe that some important results to this equation have been obtained by using the above three methods. However, when we compare the results of this paper by applying two different systematic methods with the results of [5], the exponential function solutions and elliptic function solutions as a new aspect have been proposed to the literature. All these methods enrich the study of the (2+1)-dimensional KP equation.

The -expansion method allows us to express the exact solutions of NLDEs as a polynomial of , in which satisfies the ODE (6). We can determine the degree of the polynomial through the homogeneous balance and obtain the values of the undetermined coefficients of the polynomial via the calculations of computer software, and then we obtain the exact solutions. With this method, we obtained seven solutions to the mentioned equation in which rational solution is equivalent to if we consider .

With the extended complex method, we can derive meromorphic solutions of the differential equations which do not satisfy condition or are not Briot-Bouquet equation [41]. Therefore, more NLDEs in mathematical physics can be solved by the extended complex method. Using the indeterminate forms of the solutions, we are able to seek meromorphic solutions for the differential equation with a pole at , and then we can derive meromorphic solutions , , for the differential equation with an arbitrary pole.

In this article, we search for analytical solutions of the (2+1)-dimensional KP equation by two different systematic methods. By the -expansion method and extended complex method, we obtain five kinds of exact solutions. The results demonstrate that these two methods are efficient and direct methods allowing us to do complicated and tedious algebraic calculation.

#### Data Availability

The data used to support the findings of this study are included within the article.

#### Conflicts of Interest

The authors declare that they have no competing interests.

#### Acknowledgments

This work is supported by the NSF of China (11901111, 11701111), the NSF of Guangdong Province (2016A030310257), and Visiting Scholar Program of Chern Institute of Mathematics.

#### References

- L. Gai, S. Bilige, and Y. Jie, “The exact solutions and approximate analytic solutions of the (2+1)-dimensional KP equation based on symmetry method,”
*SpringerPlus*, vol. 5, no. 1, 2016. View at: Google Scholar - V. E. Zakharov, “Shock waves propagated on solitons on the surface of a fluid, Radiophys,”
*Quantum Electronics*, vol. 29, no. 9, pp. 813–817, 1986. View at: Google Scholar | MathSciNet - U. K. Samanta, A. Saha, and P. Chatterjee, “Bifurcations of dust ion acoustic travelling waves in a magnetized dusty plasma with a q-nonextensive electron velocity distribution,”
*Physics of Plasmas*, vol. 20, no. 2, Article ID 022111, 2013. View at: Google Scholar - A. Saha, N. Pal, and P. Chatterjee, “Bifurcation and quasiperiodic behaviors of ion acoustic waves in magnetoplasmas with nonthermal electrons featuring tsallis distribution,”
*Brazilian Journal of Physics*, vol. 45, no. 3, pp. 325–333, 2015. View at: Publisher Site | Google Scholar - A. Borhanifar, H. Jafari, and S. A. Karimi, “New solitons and periodic solutions for the Kadomtsev-Petviashvili equation,”
*Journal of Nonlinear Sciences and Applications*, vol. 1, no. 4, pp. 224–229, 2008. View at: Publisher Site | Google Scholar - K. Khan and M. Ali Akbar, “Exact traveling wave solutions of Kadomtsev–Petviashvili equation,”
*Journal of the Egyptian Mathematical Society*, vol. 23, no. 2, pp. 278–281, 2015. View at: Publisher Site | Google Scholar - X. Zhang, Y. Chen, and X. Tang, “Rogue wave and a pair of resonance stripe solitons to KP equation,”
*Computers & Mathematics with Applications*, vol. 76, no. 8, pp. 1938–1949, 2018. View at: Publisher Site | Google Scholar | MathSciNet - A. R. Adem, “Symbolic computation on exact solutions of a coupled Kadomtsev-Petviashvili equation: Lie symmetry analysis and extended tanh method,”
*Computers & Mathematics with Applications. An International Journal*, vol. 74, no. 8, pp. 1897–1902, 2017. View at: Publisher Site | Google Scholar | MathSciNet - C. M. Khalique, “On the solutions and conservation laws of a coupled kadomtsev-petviashvili equation,”
*Journal of Applied Mathematics*, vol. 2013, Article ID 741780, 7 pages, 2013. View at: Publisher Site | Google Scholar - H.-Q. Zhao and W.-X. Ma, “Mixed lump-kink solutions to the KP equation,”
*Computers & Mathematics with Applications. An International Journal*, vol. 74, no. 6, pp. 1399–1405, 2017. View at: Publisher Site | Google Scholar | MathSciNet - Z. Ma, J. Chen, and J. Fei, “Lump and line soliton pairs to a ( 2 + 1 ) -dimensional integrable Kadomtsev–Petviashvili equation,”
*Computers & Mathematics with Applications*, vol. 76, no. 5, pp. 1130–1138, 2018. View at: Publisher Site | Google Scholar - J. Jiang, L. Liu, and Y. Wu, “Positive solutions to singular fractional differential system with coupled boundary conditions,”
*Communications in Nonlinear Science and Numerical Simulation*, vol. 18, no. 11, pp. 3061–3074, 2013. View at: Publisher Site | Google Scholar | MathSciNet - J. Liu and Z. Zhao, “Existence of positive solutions to a singular boundary-value problem using variational methods,”
*Electronic Journal of Differential Equations*, vol. 135, 9 pages, 2014. View at: Google Scholar | MathSciNet - Y. Xu and H. Zhang, “Positive solutions of an infinite boundary value problem for nth-order nonlinear impulsive singular integro-differential equations in Banach spaces,”
*Applied Mathematics and Computation*, vol. 218, no. 9, pp. 5806–5818, 2012. View at: Publisher Site | Google Scholar - L. Gao, D. Wang, and G. Wang, “Further results on exponential stability for impulsive switched nonlinear time-delay systems with delayed impulse effects,”
*Applied Mathematics and Computation*, vol. 268, pp. 186–200, 2015. View at: Publisher Site | Google Scholar - F. Sun, L. Liu, and Y. Wu, “Finite time blow-up for a class of parabolic or pseudo-parabolic equations,”
*Computers & Mathematics with Applications*, vol. 75, no. 10, pp. 3685–3701, 2018. View at: Publisher Site | Google Scholar | MathSciNet - Q. Gao, F. Li, and Y. Wang, “Blow-up of the solution for higher-order Kirchhoff-type equations with nonlinear dissipation,”
*Central European Journal of Mathematics*, vol. 9, no. 3, pp. 686–698, 2011. View at: Publisher Site | Google Scholar | MathSciNet - X. Hao, H. Wang, L. Liu, and Y. Cui, “Positive solutions for a system of nonlinear fractional nonlocal boundary value problems with parameters and
*p*-Laplacian operator,”*Boundary Value Problems*, vol. 2017, no. 1, Article ID 182, 2017. View at: Publisher Site | Google Scholar - J. Jiang, L. Liu, and Y. Wu, “Symmetric positive solutions to singular system with multi-point coupled boundary conditions,”
*Applied Mathematics and Computation*, vol. 220, pp. 536–548, 2013. View at: Publisher Site | Google Scholar | MathSciNet - Y. Wang and Z. Zhao, “Existence and multiplicity of solutions for a second-order impulsive differential equation via variational methods,”
*Advances in Difference Equations*, Paper No. 46, 9 pages, 2017. View at: Publisher Site | Google Scholar | MathSciNet - M. Shao and A. Mao, “Multiplicity of solutions to Schrödinger-Poisson system with concave-convex nonlinearities,”
*Applied Mathematics Letters*, vol. 83, pp. 212–218, 2018. View at: Publisher Site | Google Scholar | MathSciNet - L. Liu, F. Sun, X. Zhang, and Y. Wu, “Bifurcation analysis for a singular differential system with two parameters via to topological degree theory,”
*Nonlinear Analysis: Modelling and Control*, vol. 22, no. 1, pp. 31–50, 2017. View at: Publisher Site | Google Scholar - F. Sun, L. Liu, X. Zhang, and Y. Wu, “Spectral analysis for a singular differential system with integral boundary conditions,”
*Mediterranean Journal of Mathematics*, vol. 13, no. 6, pp. 4763–4782, 2016. View at: Publisher Site | Google Scholar | MathSciNet - Y. Wang, L. Liu, X. Zhang, and Y. Wu, “Positive solutions of an abstract fractional semipositone differential system model for bioprocesses of HIV infection,”
*Applied Mathematics and Computation*, vol. 258, pp. 312–324, 2015. View at: Publisher Site | Google Scholar | MathSciNet - X. G. Zhang, L. S. Liu, Y. H. Wu, and B. Wiwatanapataphee, “The spectral analysis for a singular fractional differential equation with a signed measure,”
*Applied Mathematics and Computation*, vol. 257, pp. 252–263, 2015. View at: Publisher Site | Google Scholar | MathSciNet - X. Lin and Z. Zhao, “Iterative technique for a third-order differential equation with three-point nonlinear boundary value conditions,”
*Electronic Journal of Qualitative Theory of Differential Equations*, vol. 2016, 2016. View at: Publisher Site | Google Scholar - X. Zhang, L. Liu, and Y. Wu, “The uniqueness of positive solution for a singular fractional differential system involving derivatives,”
*Communications in Nonlinear Science and Numerical Simulation*, vol. 18, no. 6, pp. 1400–1409, 2013. View at: Publisher Site | Google Scholar - W. X. Ma, J. Li, and C. M. Khalique, “A study on lump solutions to a generalized hirota-satsuma-ito equation in (2+1)-dimensions,”
*Complexity*, vol. 2018, Article ID 9059858, 2018. View at: Google Scholar | MathSciNet - S.-T. Chen and W.-X. Ma, “Exact solutions to a generalized bogoyavlensky-konopelchenko equation via maple symbolic computations,”
*Complexity*, vol. 2019, Article ID 8787460, 2019. View at: Google Scholar - H. Roshid, “Lump solutions to a (3+1)-dimensional potential-yu–toda–sasa–fukuyama (YTSF) like equation,”
*International Journal of Applied and Computational Mathematics*, vol. 3, no. S1, pp. 1455–1461, 2017. View at: Publisher Site | Google Scholar - H. Roshid and W. X. Ma, “Dynamics of mixed lump-solitary waves of an extended (2+1)-dimensional shallow water wave model,”
*Physics Letters A*, vol. 382, no. 45, pp. 3262–3268, 2014. View at: Publisher Site | Google Scholar | MathSciNet - M. M. Roshid and H.-O. Roshid, “Exact and explicit traveling wave solutions to two nonlinear evolution equations which describe incompressible viscoelastic Kelvin-Voigt fluid,”
*Heliyon*, vol. 4, article no. e00756, 2018. View at: Google Scholar - H.-O. Roshid, M. R. Kabir, R. C. Bhowmik, and B. K. Datta, “Investigation of Solitary wave solutions for Vakhnenko-Parkes equation via exp-function and Exp(−
(*ϕ*))-expansion method,”*ξ**SpringerPlus*, vol. 3, no. 1, p. 692, 2014. View at: Publisher Site | Google Scholar - H. O. Roshid, M. N. Alam, and M. A. Akbar, “Traveling wave solutions for fifth order (1+1)-dimensional Kaup-Keperschmidt equation with the help of Exp(-
*ϕη*)-expansion method,”*Walailak Journal of Science and Technology*, vol. 12, no. 11, pp. 1063–1073, 2015. View at: Google Scholar - H.-O. Roshid and M. Azizur Rahman, “The exp(-
*ϕ*(*ξ*))-expansion method with application in the (1+1)-dimensional classical Boussinesq equations,”*Results in Physics*, vol. 4, pp. 150–155, 2014. View at: Publisher Site | Google Scholar - K. Khan and M. A. Akbar, “The exp(-
*ϕ*(*ξ*))-expansion method for finding traveling wave solutions of Vakhnenko-Parkes equation,”*International Journal of Dynamical Systems and Differential Equations*, vol. 5, no. 1, pp. 72–83, 2014. View at: Publisher Site | Google Scholar | MathSciNet - N. Kadkhoda and H. Jafari, “Analytical solutions of the Gerdjikov-Ivanov equation by using exp(-
*φ*(*ξ*))-expansion method,”*Optik*, vol. 139, pp. 72–76, 2017. View at: Google Scholar - Y. Gu and J. Qi, “Symmetry reduction and exact solutions of two higher-dimensional nonlinear evolution equations,”
*Journal of Inequalities and Applications*, vol. 2017, no. 1, article 314, 2017. View at: Publisher Site | Google Scholar | MathSciNet - H. Jafari, N. Kadkhoda, and D. Baleanu, “Fractional Lie group method of the time-fractional Boussinesq equation,”
*Nonlinear Dynamics*, vol. 81, no. 3, pp. 1569–1574, 2015. View at: Publisher Site | Google Scholar | MathSciNet - H. Jafari, N. Kadkhoda, M. Azadi, and M. Yaghobi, “Group classification of the time-fractional Kaup-Kupershmidt equation,”
*Scientia Iranica*, vol. 24, no. 1, pp. 302–307, 2017. View at: Publisher Site | Google Scholar - W. Yuan, Y. Li, and J. Lin, “Meromorphic solutions of an auxiliary ordinary differential equation using complex method,”
*Mathematical Methods in the Applied Sciences*, vol. 36, no. 13, pp. 1776–1782, 2013. View at: Publisher Site | Google Scholar | MathSciNet - W. J. Yuan, Y. D. Shang, Y. Huang, and H. Wang, “The representation of meromorphic solutions to certain ordinary differential equations and its applications,”
*Science China Mathematics*, vol. 43, no. 6, pp. 563–575, 2013. View at: Publisher Site | Google Scholar - W. Yuan, Y. Wu, Q. Chen, and Y. Huang, “All meromorphic solutions for two forms of odd order algebraic differential equations and its applications,”
*Applied Mathematics and Computation*, vol. 240, pp. 240–251, 2014. View at: Publisher Site | Google Scholar | MathSciNet - W. Yuan, F. Meng, Y. Huang, and Y. Wu, “All traveling wave exact solutions of the variant Boussinesq equations,”
*Applied Mathematics and Computation*, vol. 268, pp. 865–872, 2015. View at: Publisher Site | Google Scholar | MathSciNet - Y. Gu, W. Yuan, N. Aminakbari, and Q. Jiang, “Exact solutions of the vakhnenko-parkes equation with complex method,”
*Journal of Function Spaces*, vol. 2017, Article ID 6521357, 6 pages, 2017. View at: Publisher Site | Google Scholar - Y. Gu, W. Yuan, N. Aminakbari, and J. Lin, “Meromorphic solutions of some algebraic differential equations related Painlevé equation IV and its applications,”
*Mathematical Methods in the Applied Sciences*, vol. 41, no. 10, pp. 3832–3840, 2018. View at: Publisher Site | Google Scholar | MathSciNet - Y. Y. Gu, N. Aminakbari, W. J. Yuan, and Y. H. Wu, “Meromorphic solutions of a class of algebraic differential equations related to Painlevé equation III,”
*Houston Journal of Mathematics*, vol. 43, no. 4, pp. 1045–1055, 2017. View at: Google Scholar | MathSciNet - Y. Y. Gu, B. M. Deng, and J. M. Lin, “Exact traveling wave solutions to the (2+1)-dimensional Jaulent-Miodek equation,”
*Advances in Mathematical Physics*, vol. 2018, Article ID 5971646, 9 pages, 2018. View at: Publisher Site | Google Scholar - Y. Gu, “A note on the fractional generalized higher order KdV equation,”
*Journal of Function Spaces*, vol. 2018, 6 pages, 2018. View at: Publisher Site | Google Scholar - Y. Gu, X. Zheng, and F. Meng, “Painlevé analysis and abundant meromorphic solutions of a class of nonlinear algebraic differential equations,”
*Mathematical Problems in Engineering*, vol. 2019, Article ID 9210725, 11 pages, 2019. View at: Publisher Site | Google Scholar - S. Lang,
*Elliptic Functions*, Springer, New York, NY, USA, 2nd edition, 1987. View at: MathSciNet

#### Copyright

Copyright © 2019 Yongyi Gu and Fanning Meng. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.