The First Integral Method to the Nonlinear Schrodinger Equations in Higher Dimensions
Abstract
The first integral method introduced by Feng is adopted for solving some important nonlinear partial differential equations, including the (2 + 1)-dimensional hyperbolic nonlinear Schrodinger (HNLS) equation, the generalized nonlinear Schrodinger (GNLS) equation with a source, and the higher-order nonlinear Schrodinger equation in nonlinear optical fibers. This method provides polynomial first integrals for autonomous planar systems. Through the established first integrals, exact traveling wave solutions are formally derived in a concise manner.
1. Introduction
It is well known that nonlinear complex physical phenomena are related to nonlinear partial differential equations (NLPDEs) which are involved in many fields from physics to biology, chemistry, mechanics, etc. As mathematical models of the phenomena, the investigation of exact solutions of NLPDEs will help us to understand these phenomena better. Many effective methods for obtaining exact solutions of NLPDEs have been established and developed, such as the Lie point symmetries method [1], the exp-function method [2, 3], the sine-cosine method [4, 5], the extended tanh-coth method [6, 7], the projective Riccati equation method [8, 9], and so on.
The first integral method was first proposed by Feng in [10] in solving Burgers-KdV equation which is based on the ring theory of commutative algebra. Recently, this useful method has been widely used by many such as in [11–21] and by the references therein. In Section 2, we have described this method for finding exact travelling wave solutions of nonlinear evolution equations. In Section 3, we have illustrated this method in detail with the (2+1)-dimensional hyperbolic nonlinear Schrodinger (HNLS) equation, the generalized nonlinear Schrodinger (GNLS) equation with a source, and the higher-order nonlinear Schrodinger equation in nonlinear optical fibers. In Section 4, we have given some conclusions.
2. The First Integral Method
Raslan in [22] has summarized the first integral method in the following steps.
Step 1. Using a wave variable ξ = x − ct + ε, where ε is an arbitrary constant, (1) can be written in the following nonlinear ordinary differential equation (ODE):
Step 2. Assume that the solution of ODE (2) can be written as
Step 3. We introduced new independent variables
Step 4. According to the qualitative theory of ODEs [23], if we can find the integrals to (5a) and (5b) under the same conditions, then the general solution to (5a) and (5b) can be found directly. However, in general, it is really difficult to realize this even for one first integral, because for a given plane autonomous system, there is no systematic theory that can tell us how to find its first integrals, nor is there a logical way for telling us what these first integrals are.
We will apply the division theorem to obtain one first integral to (5a) and (5b) which reduces (2) to a first-order integrable ODE.
An exact solution to (1) is then obtained by solving this equation.
Let us now recall the division theorem for two variables in the complex domain C(w, z).
Theorem 1 (division theorem). Suppose that P(w, z) and Q(w, z) are polynomials in C(w, z), and P(w, z) is irreducible in C(w, z). If Q(w, z) vanishes at all zero points of P(w, z), then there exists a polynomial G(w, z) in C(w, z) such that
The division theorem follows immediately from the Hilbert-Nullstellensatz Theorem [24].
Theorem 2 (Hilbert-Nullstellensatz theorem). Let k be a field and L an algebraic closure of k.
- (1)
Every ideal γ of k[X1, …, Xn] not containing 1 admits at least one zero in Ln.
- (2)
Let x = (x1, …, xn), y = (y1, …, yn) be two elements of Ln; for the set of polynomials of k[X1, …, Xn] zero at x to be identical with the set of polynomials of k[X1, …, Xn] zero at y it is necessary and sufficient that there exists a k-automorphism s of L such that yi = s (xi) for 1 ≤ i ≤ n.
- (3)
For an ideal α of k[X1, …, Xn] to be maximal, it is necessary and sufficient that there exists an x in Ln such that α is the set of polynomials of k[X1, …, Xn] to be zero at x.
- (4)
For a polynomial Q of k[X1, …, Xn] to be zero on the set of zeros in Ln of an ideal γ of k[X1, …, Xn], it is necessary and sufficient that there exists an integer m≻0 such that Qm ∈ γ.
3. Applications
In this section, we have investigated three NPDEs using the first integral method for the first time.
3.1. The (2+1)-Dimensional Hyperbolic Nonlinear Schrodinger Equation
Case 1. Suppose that m = 1, by equating the coefficients of Yi (i = 2, 1, 0) on both sides of (11), we have
Balancing the degrees of h(X) and a0(X), we have concluded that deg (h(X)) = 1 only. Suppose that h(X) = AX + B and A ≠ 0, we find a0(X)
Substituting a0(X), a1(X), and h(X) for (12c) and setting all the coefficients of powers X to be zero, we have obtained a system of nonlinear algebraic equations and by solving it, we have obtained
Combining (15) with (9a), we have obtained the exact solutions to (9a) ad (9b). The exact traveling wave solutions to the (2+1)-dimensional hyperbolic nonlinear Schrodinger equation (7) can be written as
Case 2. Assume that m = 2, by equating the coefficients of Yi( i = 3, 2, 1, 0 ) on both sides of (11), we have
In this case, let us assume that h(X) = AX + B and A ≠ 0, then we find a1(X) and a0(X) as follows:
3.2. The Generalized Nonlinear Schrodinger (GNLS) Equation with a Source
The GNLS equation (23) plays an important role in many nonlinear sciences. It arises as an asymptotic limit for a slowly varying dispersive wave envelope in a nonlinear medium. For example, its significant application in optical soliton communication plasma physics has been proved.
Furthermore, the GNLS equation enjoys many remarkable properties (e.g., bright and dark soliton solutions, Lax pair, Liouvile integrability, inverse scattering transformation, conservation laws, Backlund transformation, etc.).
Case 3. Suppose that m = 1, by equating the coefficients of Yi (i = 2, 1, 0) on both sides of (31), we have
Balancing the degrees of h(X) and a0(X), it can be concluded that deg (h(X)) = 1 only. Suppose that h(X) = AX + B, and A ≠ 0, then we find
Substituting a0(X), a1(X), and h(X) in (32c) and setting all the coefficients of powers X to be zero, we have obtained a system of nonlinear algebraic equations and by solving it, we obtain
Combining (35) with (29a), the exact solutions to (29a) and (29b) were obtained and then the exact traveling wave solutions to the generalized nonlinear Schrodinger (GNLS) equation with a source (23) can be written as
Case 4. Suppose that m = 2, by equating the coefficients of Yi (i = 3,2, 1,0) on both sides of (31), we have
In this case, it was assumed that h(X) = AX + B and A ≠ 0; then we find a1(X) and a0(X) as follows:
Substituting a0(X), a1(X), a2(X), and h(X) for (38d) and setting all the coefficients of powers X to be zero, a system of nonlinear algebraic equations was obtained and by solving it, we got
Equations (36)-(37) and (42)-(43) are new types of exact traveling wave solutions to the generalized nonlinear Schrodinger (GNLS) equation with a source (23). It could not be obtained by the methods presented in [32].
3.3. The Higher-Order Nonlinear Schrodinger Equation in Nonlinear Optical Fibers
where ψ is slowly varying envelope of the electric field, the subscripts z and t are the spatial and temporal partial derivative in retard time coordinates, and α1, α2, α3, α4, α5 are the real parameters related to the group velocity dispersion (GVD), self-phase modulation (SPM), third-order dispersion (TOD), and self-steepening and self-frequency shift arising from simulated Raman scattering, respectively. Some properties of the equation, as well as many versions of it have been studied [33–39]. Up to now, the bright, dark and the combined bright and dark solitary waves and periodic waves were found of (43) and its special case.
Case 5. Suppose that m = 1, by equating the coefficients of Yi (i = 2,1, 0) on both sides of (51), we have
Case 6. Suppose that m = 2, by equating the coefficients of Yi (i = 3,2, 1,0) on both sides of (51), we have
Comparing these results with Liu’s results [39], it can be seen that the solutions here are new.
4. Conclusion
Searching for first integrals of nonlinear ODEs is one of the most important problems since they permit us to solve a nonlinear differential equation by quadratures. Applying the first integral method, which is based on the ring theory of commutative algebra, some new exact traveling wave solutions to the (2+1)-dimensional hyperbolic nonlinear Schrodinger (HNLS) equation, generalized nonlinear Schrodinger (GNLS) equation with a source and higher-order nonlinear Schrodinger equation in nonlinear optical fibers were established.
These solutions may be important for the explanation of some practical physical problems.
The first integral method described herein is not only efficient but also has the merit of being widely applicable.
Therefore, this method can be applied to other nonlinear evolution equations and this will be done elsewhere.
Acknowledgment
The author would like to thank the referees for their useful comments which led to some improvements of the current paper.