“…This equation arises from some problems associated to mathematical models for the study of pattern formation in physics and mechanics, for example, the well-known extended Fisher-Kolmogorov equation proposed by Coulet, Elphick and Repeaux [4], in the study of phase transitions, the fourth-order elastic beam equation in describing a large class of elastic deflection [13], the Swift-Hohenberg equation which is a general model for patternforming process derived in [5] to describe vandom thermal fluctuations in the Boussinesque equation and the propagation of lazers [7]. With the aid of variational methods and the critical point theory, the existence and the multiplicity of homoclinic solutions for (F ) have been extensively investigated in the literature over the past years, see, e.g., [1,2,3,8,9,10,15,11,12,14,16,17,18,19,20] and the references therein. Many results are on the existence of homoclinic solutions to equation (F ) when a(x) and f (x, u) are independent of x or periodic in x; see [1,2,3,8,14] and the references cited therein.…”