stochastic soliton like solution - kdv equation

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    The stochastic soliton-like solutionsof stochastic KdV equations

    Yong Chen a,b,c,*, Qi Wang b,d, Biao Li b,d

    a Department of Mathematics, Ningbo University, Ningbo 315211, Chinab Key Laboratory of Mathematics Mechanization, Chinese Academy of Sciences, Beijing 100080, China

    c Department of Physics, Shanghai Jiao-Tong University, Shanghai 200030, Chinad Department of Applied Mathematics, Dalian University of Technology, Dalian 116024, China

    Accepted 21 June 2004

    Communicated by Prof. M. Wadati

    Abstract

    By means of a generalized method and symbolic computation, we consider a stochastic KdV equation Ut+

    f(t)UUx+ g(t)Uxxx= W(t)R(t, U, Ux, Uxxx). We construct new and more general formal solutions. At the same

    time, we recover all the solutions found by Xie [Phys. Lett. A 310 (2003) 161]. The solutions obtained include the non-

    travelling wave and coefficient functions stochastic soliton-like solutions, singular stochastic soliton-like solutions,

    stochastic triangular functions solutions.

    2004 Elsevier Ltd. All rights reserved.

    1. Introduction

    As is well known, the motion of long, unidirectional, weakly nonlinear water waves on a channel can be described by

    the Kortewegde Vries (KdV) equation. When the surface of the fluid is submitted to a nonconstant pressure, or when

    the bottom of the layer is not flat, a forcing term has to be added to the equation. This term is given by the gradient

    of the exterior pressure or of the function whose graph defines the bottom. We are interested in the case when the forc-

    ing term is random, which is a very natural approach if it is assumed that the exterior pressure is generated by a tur-

    bulent velocity field for instance. We also assume that this random force is of white noise type[15]. In 1983, for the first

    time M. Wadati answers an interesting question, how does external noise affect the motion of solitons?. In [1],theKdV equation under Gaussian noise is studied and it is showed that a soliton under Gaussian noise satisfies a diffusion

    equation in transformed coordinates; the deformation of the soliton during the propagation is explicitly obtained; the

    phenomenon is designated as the diffusion of soliton. In 1990, a nonlinear partial differential equation which describes

    wave propagations in random media is presented by Wadati[2]. The stochastic equation (17) in[2]is useful for study of

    similar problem in hydrodynamics and plasmas physics. Recently, the stochastic KdV equation arises when modelling

    0960-0779/$ - see front matter 2004 Elsevier Ltd. All rights reserved.

    doi:10.1016/j.chaos.2004.06.049

    * Corresponding author. Address: Department of Mathematics, Ningbo University, Ningbo 315211, China.

    E-mail address: [email protected](Y. Chen).

    Chaos, Solitons and Fractals 23 (2005) 14651473

    www.elsevier.com/locate/chaos

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    the propagation of weakly nonlinear waves in a noisy plasma [26]. The remarkable achievement (see[16]and refer-

    ences for detail) of the study of stochastic partial differential equation have been obtained, for example, de Bouard and

    Debussche[6] use function space similar to those introduced by Bourgain to prove well posedness results for the KdV

    equation inL2-function and obtain the global existence ofL2(R) solution when the covariance operator of the noise is

    HilbertSchmidt in L2(R). Holden et al. [7]gave while noise functional approach to research stochastic partial differ-

    ential equations in Wick version. More recently, based on the theory in [7], using Hermite transform and the homog-

    enous balance method, Xie studied Wick-type stochastic KdV equation and obtained stochastic soliton solution of thisequation[8].

    In this paper, we would like to further extended the method presented by Fan [911] and recently improved by

    Chen et al. [1214], to find stochastic soliton-like solutions of a Wick-type stochastic KdV equation as the following

    form[8]:

    UtftU}Ux gtUxxx Wt}R}t;U;Ux;Uxxx 1:1

    which is the perturbation of the KdV equation with variable coefficients

    utftuux gtuxxx 0 1:2

    by random force W(t)R(R, U, Ux, Uxxx), where f(t) and g(t) are functions of t, W(t) is Gaussian white noise, i.e.,

    Wt _Bt and B(t) is a Brownian motion, R(u, ux, uxxx) = auux buxxx is a functional ofu, ux and uxxx for someconstantsa,b and R is the Wick version of the functionalR. For more detail about the exchange between Wick-type

    stochastic equation and common partial differential equation, the reader is advised to see the remarkable achievement

    by Holden et al. [7] and the second section of Ref. [8] by Xie. As a result, we construct new and more general formal

    solutions for Eq.(1), which include the nontravelling wave and coefficient function s stochastic soliton-like solutions,

    singular stochastic soliton-like solutions, stochastic triangular functions solutions.

    The rest of this paper is organized as follows. In Section 2, we establish a generalized method. In Section 3, we apply

    the generalized method to a stochastic KdV equation and obtain some exact analytical solutions for this model. A short

    summary and discussion are given in final.

    2. Summary of the generalized method

    In the following we would like to outline the main steps of our general method:

    Step 1. For a given nonlinear partial differential equation (NPDE) system with some physical fields ui(x,y, t)

    (i= 1, . . . , n) in three variables x,y, t,

    Fiui; uit; uix; uiy; uitt; uixt; uiyt; uixx; uiyy; uixy; . . . 0: 2:1

    We express the solutions of the NPDE by the new more general ansatz

    uin ai0 Xmij1

    aij/j bij/j1

    ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiX4q0

    hq/q

    vuut

    80; h4 0: 2:5

    b. Kink shaped soliton-like solutions.

    / ffiffiffiffiffiffiffiffiffiffiffiffi

    h22h4

    r tanh

    ffiffiffiffiffiffiffiffiffi h2

    2

    r n

    !; h0 h

    22

    4h4; h1 h3 0; h2 0: 2:6

    c. Soliton-like solutions.

    / h2 sech2 1

    2

    ffiffiffiffiffih2

    p n

    2ffiffiffiffiffiffiffiffiffih2h4

    p tanh 1

    2

    ffiffiffiffiffih2

    p n

    h3 ; h0 h1 0; h2 >0: 2:7(ii) Jacobi and Weierstrass doubly-like periodic solutions.

    / ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffi

    h2m2h42m2 1

    s cn

    ffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffih2

    2m2 1

    r n

    !; h4 0; h0 h

    22m

    21 m2h42m2 12

    ; 2:8

    / ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffim2h42 m2

    s dn

    ffiffiffiffiffiffiffiffiffiffiffiffi ffiffih2

    2 m2r

    n

    !; h4 0; h0 h

    221 m2

    h42 m22; 2:9

    / ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffi

    h2m2h4m2 1

    s sn

    ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffi h2m2 1

    r n

    !; h4 >0; h2 0; 2:11

    whereg2 4h1

    h3 and g3 4h0

    h3 are called invariants of Weierstrass elliptic function. The Jacobi elliptic functions aredoubly periodic and possess properties of triangular functions:

    sn2n cn2n 1; dn2n 1 m2sn2n;snn0 cnndnn; cnn0 snn; dnn0 m2snncnn:

    When m ! 1, the Jacobi functions degenerate to the hyperbolic functions, i.e.snn ! tanh n; cnn ! sechn;

    whenm ! 0, the Jacobi functions degenerate to the triangular functions, i.e.snn ! sin n; cnn ! cos n:

    The more detailed notations for the Weierstrass and Jacobi elliptic functions can be found in Refs. [19,20].

    Y. Chen et al. / Chaos, Solitons and Fractals 23 (2005) 14651473 1467

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    Remark 1

    1. Generalization: The method proposed here is more general than the method [911] by Fan, the method [1214]

    improved by Chen et al. and the method [15] improved by E. Yomba. Firstly, compared with the method [911]

    and the improved method [1214] the restriction on n(x,y, t) as merely a linear function x,y, t and the restriction

    on the coefficients ai0, aij, bij (i= 1,2, . . . ; j= 1,2, . . . , mi) as constants are removed. Secondly, compared with the

    improved method [15] by E. Yomba, the Eq. (2.3) that the new variable /= /(n) satisfies is more general. More

    importantly, we add terms bij/j1

    ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiP4q0hq/

    qq

    in new ansatz (2.2), so more types of solutions would be expected

    for some equations.

    2. Feasibility: For the generalization of the ansatz, naturally more complicated computation is expected than ever

    before. Even if the availability of computer symbolic systems like Maple or Mathematica allows us to perform

    the complicated and tedious algebraic calculation and differentiation on a computer, in general it is very difficult,

    sometime impossible, to solve the set of over-determined partial differential equations in (step 3). As the calculation

    goes on, in order to drastically simplify the work or make the work feasible, we often choose special function forms

    for ai0, aij, bij(i= 1,2, . . . ; j= 1,2, . . . , mi) and n, on a trial-and-error basis.

    3. Further extendable: In fact, We naturally present a more general a ansatz, which reads,

    uin ai0 Xmij1

    aij/j bij/j fij/j1 ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiXr

    q0hq/

    qvuut kij ffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiPr

    q0hq/

    qsuj

    8>>>>>>>:9>>>>=>>>>;; 2:12

    where ai0, aij, bij,fij, kij (i= 1,2, . . . ; j= 1,2, . . . , mi) and n are differentiable function to be determined later. When

    ai0, aij, bij,fij, kij(i= 1,2, . . . ; j= 1,2, . . . , mi) are constants and n is linear function with respect to x,y and t in the above

    ansatz, we have studied in Refs. [1618]. Therefore, for some nonlinear equations, more types of solutions would be

    expected.

    3. The stochastic soliton solutions of stochastic KdV equations

    In this section, we will give exact solutions of Eq.(1.1)by the generalized method. Taking the Hermite transform of(1.1), we get the equationfUtt;x;z ht;z eUt;x;z eUxt;x;z st;z eUxxxt;x;z 0; 3:1where ht;z ft a eWt;z, st;z gt b eWt;z, the Hermite transformation of W(t) is defined byeWt;z P1k1gktzk when z= (z1,z2, . . . ,)2 (CN)c is parameter. We first solve Eq.(3.1).

    According to the generalized method, we suppose that the solutions of(3.1)are the form

    eUt;x;z a0 a1/n b1 ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffiffih0 h1/n h2/2n h3/3n h4/4nq a2/2n b2/nffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiffiffiffiffiffih0 h1/n h2/2n h3/3n h4/4n

    q ; 3:2

    wherea0= a0(t, z), a1= a1(t, z), a2= a2(t, z), b1= b1(t, z), b2= b2(t, z),n= xp(t, z) + q(t, z) and /(n) satisfy(2.3).

    Then substituting(3.2) and (2.3)into(3.1), collecting coefficients of monomials of/(n), ffiffiffiffiffiffiffiffiffiffiffiffiffi ffiffiffiffiffiffiffiffiP4q0hq/qq and x of theresulting systems numerator (Notice that h(t, z),s(t, z),a0(t, z),a1(t, z),a2(t, z),b1(t, z),b2(t, z),p(t, z),q(t, z) are all inde-

    pendent ofx), then setting each coefficients to zero, we obtain the following over-determined PDEs system.

    8ht;zpt;za0t;zb2t;zh2 60h4st;zpt;z3b1t;zh1 10ht;zpt;za1t;zb2t;zh1 144h4st;zpt;z3b2t;zh0 6h3b1t;z o

    otqt;z 8ht;zpt;zb1t;za1t;zh2 32st;zpt;z3b2t;zh22

    10ht;zpt;zb1t;za2t;zh1 30st;zpt;z3b1t;zh2h3 8b2t;z ootqt;z

    h2

    12ht;zpt;za2t;zb2t;zh0 4 oota2t;z 84st;zpt;z3b2t;zh1h3 6h3ht;zpt;za0t;zb1t;z 0;

    3:3

    1468 Y. Chen et al. / Chaos, Solitons and Fractals 23 (2005) 14651473

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    12h4b2t;z ootpt;z 0; 3:4

    2 o

    otpt;z

    2h0b2t;z b1t;zh1 0; 3:5

    4ht;zpt;zb1t;zb2t;zh0 4ht;zpt;za0t;za1t;z 4st;zpt;z3a1t;zh2 2ht;zpt;zb1t;z2h1 12st;zpt;z3a2t;zh1 4 o

    otb1t;z 4a1t;z o

    otqt;z 0; 3:6

    180h4st;zpt;z3b2t;zh1 8h4ht;zpt;za0t;zb1t;z 12ht;zpt;zb1t;za2t;zh2 14ht;zpt;za2t;zb2t;zh1 10h3ht;zpt;za0t;zb2t;z 10h3ht;zpt;zb1t;za1t;z 80h4st;zpt;z3b1t;zh2 8h4b1t;z o

    otqt;z 130st;zpt;z3b2t;zh2h3

    12ht;zpt;za1t;zb2t;zh2 10h3b2t;z ootqt;z 30st;zpt;z3b1t;zh23 0; 3:7

    2

    o

    otpt;z 4h2b2t;z 3h3b1t;z 0; 3:82

    o

    otpt;z

    2b1t;zh2 3h1b2t;z 0; 3:9

    30st;zpt;z3b2t;zh1h2 4ht;zpt;za0t;zb1t;zh2 48st;zpt;z3b1t;zh0h4 60st;zpt;z3b2t;zh3h0 6ht;zpt;za0t;zb2t;zh1 18st;zpt;z3b1t;zh1h3 8ht;zpt;zb2t;za1t;zh0 8ht;zpt;zb1t;za2t;zh0 4 o

    ota1t;z 4st;zpt;z3b1t;zh22

    4b1t;z oot

    qt;z

    h2 6ht;zpt;zb1t;za1t;zh1 6b2t;zh1 ootqt;z 0; 3:10

    4a1t;z ootpt;z 0; 3:11

    8pt;z12h4a2t;zst;zpt;z2 ht;za2t;z2 ht;zb1t;z2h4 8pt;z2h3ht;zb1t;zb2t;z ht;zb2t;z2h2 0; 3:12

    6pt;z4pt;z2h4st;za1t;z 10pt;z2h3st;za2t;z 6pt;zht;zb2t;z2h1 2ht;za1t;za2t;z 6pt;z2ht;zb1t;zb2t;zh2 h3ht;zb1t;z2 0; 3:13

    12ht;zpt;zb2t;z2h4 0; 3:14

    20h4pt;zb2t;z12pt;z2

    h4st;z a2t;zht;z 0; 3:1510ht;zpt;zb2t;zh3b2t;z 2h4b1t;z 0; 3:16

    8a2t;z ootpt;z 0; 3:17

    4o

    ota0t;z 4ht;zpt;za1t;zb1t;zh0 12st;zpt;z3b1t;zh3h0 3st;zpt;z3b2t;zh21

    4ht;zpt;za0t;zb2t;zh0 2b1t;z ootqt;z

    h1 2ht;zpt;za0t;zb1t;zh1

    2st;zpt;z3b1t;zh1h2 4b2t;z ootqt;z

    h0 16st;zpt;z3b2t;zh2h0 0; 3:18

    Y. Chen et al. / Chaos, Solitons and Fractals 23 (2005) 14651473 1469

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    4ht;zpt;zb2t;z2h0 8ht;zpt;zb1t;zb2t;zh1 4ht;zpt;za1t;z2 8a2t;z oot

    qt;z

    8ht;zpt;za0t;za2t;z 12h3st;zpt;z3a1t;z 4 ootb2t;z 32st;zpt;z3a2t;zh2

    4h

    t;z

    p

    t;z

    b1

    t;z

    2h2

    0;

    3:19

    2

    o

    otpt;z

    4h4b1t;z 5h3b2t;z 0; 3:20

    14h3ht;zpt;zb1t;za2t;z 16ht;zpt;za2t;zb2t;zh2 12h4ht;zpt;zb1t;za1t;z 12h4ht;zpt;za0t;zb2t;z 105st;zpt;z3b2t;zh23 120h4st;zpt;z3b1t;zh3

    12h4b2t;z ootqt;z 240h4st;zpt;z3b2t;zh2 14h3ht;zpt;za1t;zb2t;z 0; 3:21

    2pt;z48p2t;zst;zb1t;zh24 168p2t;zh4st;zb2t;zh3 2pt;zht;z8h4b1t;za2t;z a1t;zb2t;z 9h3a2t;zb2t;z 0; 3:22

    Solving the system of PDEs. (3.3)(3.22)by Maple, we obtain the following two solutions.

    p F1z; h h; a1 F2z; a2 2F2z h4h3

    ; b2 0;

    a0 F3zq 3F1zRht;zdth3F3z F1z

    Rht;zdth2F2z 3F5zh3

    3h3; s 1

    3

    ht;zF2zh3F

    21z

    ;

    b1 2ffiffiffiffiffih4

    p F2zh3

    ; 3:23

    whereF1(z), . . ., F3(z) and h(t, z) are all arbitrary functions.

    Thus from(3.2) and (3.23),we obtain two families of exact solutions of Eq.(3.1)as follows. For simplicity, we omit

    polynomial-like, rational-like, triangular-like periodic solutions in this paper.Family 1. When h0= h1= h4= 0, h2> 0,

    eU1t;x;z F3z F2zh2 sech2

    ffiffiffiffih2

    p2 n

    h3

    ; 3:24

    wheren= xF1(z) + q(t, z), q(t, z), h(t, z) and s(t, z) are determined by(3.23).

    Family 2. When h0= h1= 0, h2> 0

    eU2x; t;z F3z

    F2zh2 sech2ffiffiffiffi

    h2

    p2 n

    2ffiffiffiffiffiffiffiffiffih2h4p

    tanh ffiffiffiffih2

    p2 n h3

    2F2zh4h22 sech4

    ffiffiffiffih2

    p2 n

    h3

    2ffiffiffiffiffiffiffiffiffih2h4p

    tanh ffiffiffiffih2

    p2 n h32

    2

    h52

    2

    ffiffiffiffiffih4

    ph3

    F2zsech4

    ffiffiffiffih2

    p2 n

    tanh

    ffiffiffiffih2

    p2 n

    2ffiffiffiffiffiffiffiffiffih2h4p tanh ffiffiffiffih2p2 n h32

    sech6ffiffiffiffi

    h2

    p2 n

    ffiffiffiffiffiffiffiffiffih2h4

    p

    2ffiffiffiffiffiffiffiffiffih2h4

    p tanh

    ffiffiffiffih2

    p2 n

    h3

    30BBB@

    1CCCA; 3:25wheren= xF1(z) + q(t, z), q(t, z), h(t, z) and /(t, z) determined by(3.23).

    By(3.24) and (3.25), the definition ofeW, Theorem 2.1 in Ref. [7] and exp}fBtg expfBt 12t2g (see Lemma

    2.6.16 in[6]), we have the following stochastic solitary solutions:

    Family 1.

    U1t;x F3 4 F2h2exp}

    ffiffiffiffiffih2

    p xF1 Qt

    exp}ffiffiffiffiffih2p xF1 Qt 1}2h3 ; 3:26

    1470 Y. Chen et al. / Chaos, Solitons and Fractals 23 (2005) 14651473

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    where

    Qt 3F1h3F3 F1h2F2Rftdt aBt 1

    2t2 3F4h3

    3h3;

    F1, F2, F3 and F4 are all arbitrary constants.

    Family 2.

    U2x; t F3 4exp}ffiffiffiffiffih2p nF2h2

    2ffiffiffiffiffiffiffiffiffih2h4p exp}ffiffiffiffiffih2p n 2ffiffiffiffiffiffiffiffiffih2h4p h3exp}ffiffiffiffiffih2p n h3}exp}ffiffiffiffiffih2p n 1 32exp

    }2ffiffiffiffiffih2p nh22h4F22ffiffiffiffiffiffiffiffiffih2h4p exp}ffiffiffiffiffih2p n 2ffiffiffiffiffiffiffiffiffih2h4p h3exp}ffiffiffiffiffih2p n h3}2}exp}ffiffiffiffiffih2p n 1}2h3

    32exp}ffiffiffiffiffih2p n 1}exp}2ffiffiffiffiffih2p nF2ffiffiffiffiffih4p h522

    2ffiffiffiffiffiffiffiffiffih2h4p exp}ffiffiffiffiffih2p n 2ffiffiffiffiffiffiffiffiffih2h4p h3exp}ffiffiffiffiffih2p n h3}2}exp}ffiffiffiffiffih2p n 1}3h3 128exp

    }3ffiffiffiffiffih2p nF2h4h322ffiffiffiffiffiffiffiffiffih2h4p exp}ffiffiffiffiffih2p n 2ffiffiffiffiffiffiffiffiffih2h4p h3exp}ffiffiffiffiffih2p n h3}3}exp}ffiffiffiffiffih2p n 1}3h3 ; 3:27

    where n = xF1+ Q(t),

    Qt 3F1h3F3 F1h2F2Rftdt aBt 1

    2t2 3F4h3

    3h3;

    F1, F2, F3 and F4 are all arbitrary constants.

    Remark 2

    (1) Due to the arbitrariness ofF1, F2, F3, F4and f(t), it is not difficult to verify that the solution 3.10,3.11obtained in

    [8]can be reproduced by the solution(3.26)obtained by us. But, to our knowledge, the other solutions obtained

    were not reported before.

    Fig. 1. (a) denotes a soliton-like solution scenario given by U1, where F1=F2=F3=F4=h2=h3=a = 2,ft 3sech12 ttanh1

    2t,bt 1

    2t2. (b) and (c) denote the interaction scenario of soliton-like solutions.

    Fig. 2. (a) denotes the boomerang-like soliton solution scenario given by U1, where F1=F2=F3=F4=h2=h3=a = 2, f(t) = 0,

    bt 1

    20 t

    2

    . (b) and (c) denote the interaction scenario of boomerang-like soliton solutions.

    Y. Chen et al. / Chaos, Solitons and Fractals 23 (2005) 14651473 1471

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    (2) The more general soliton-like solutions obtained by the generalized method contain the some arbitrary differen-

    tiable functions and some arbitrary constants, which may enable one to discuss the behavior of solutions as a func-

    tion of these arbitrary differentiable functions and some arbitrary constants and this also provide enough freedom

    to build up solutions that may correspond to a particular physical situation, or initial condition have some desired

    features, which means a great variation in the solutions. In order to understand the significance of these soliton-

    like solutions obtained in the paper, by choosing the special functions, we find some very interesting special solu-

    tions(3.26), which including soliton-like solutions, snake-like soliton and Boomerang-like soliton, and choose the

    solutions(3.26)to be figured. Their interaction scenario also were shown in fellow figures ( Figs. 13).

    4. Summary and discussion

    In summary, based on the generalized method and symbolic computation, by means of the theory of stochastic

    partial differential equations in Wick version [7], we study stochastic KdV equation Ut+ f(t)UUx+ g(t)Uxxx=

    W(t)R(t, U, Ux, Uxxx). Some new and more general formal solutions for Eq. (1.1) are constructed, which include

    the nontravelling wave and coefficient functions stochastic soliton-like solutions, singular stochastic soliton-like solu-

    tions, stochastic triangular functions solutions, at the same time, the results in[7]are recovered. By choosing the specialfunctions in the new and more general formal solution obtained, we would find some very interesting special solutions,

    for instance, from solution (3.26), soliton-like soliton solutions, snake-like soliton solutions, boomerage-like soliton

    solutions are fund, and their scenario and their interaction scenario are shown by the figures.

    Acknowledgments

    We would express our sincere thanks for Prof. Wadati for his valuable suggestion and kind help. The work was sup-

    ported by the National Outstanding Youth Foundation of China (no. 19925522).

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    5t 3, bt 1

    2t2. (b) and (c) denote the interaction scenario of snake-like soliton solutions.

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