Abstract-We study the asymptotic behavior of a solution of the first boundary value problem for a second-order elliptic equation in a nonconvex domain with smooth boundary in the case where a small parameter is a factor at only some of the highest derivatives and the limit equation is an ordinary differential equation. Although the limit equation has the same order as the initial equation, the problem is singulary perturbed. The asymptotic behavior of its solution is studied by the method of matched asymptotic expansions. Keywords: small parameter, asymptotic expansions.
DOI: 10.1134/S008154381305009XWe consider the first boundary value problemHere, D ⊂ R 3 is a bounded domain with boundary Γ, and L 0 is the ordinary differential operatorLet the parameter ε be positive, and let all the coefficients of equation (0.1), as well as its right-hand side, be infinitely differentiable.Assume that the boundary Γ of the domain D is smooth but the domain D is nonconvex. Assume also that there exists a bounded solution of problem (0.1), (0.2), which will be denoted by u ε (x, y, z), which satisfies the estimatewhere the constant C is independent of ε. (This condition holds, for example, if a(x, x, z) ≤ α < 0.) Problems for elliptic equations with a small parameter at the highest derivatives were studied by different authors [1][2][3]. These papers were devoted to the case when the order of the limit equation was less than the order of the original equation. This fact, in particular, resulted in the singularity of the problem; i.e., the increasing appearance of singularities in the coefficients of the standard expansion with the growth of the approximation order.