A mollifier approach to regularize a Cauchy problem for the inhomogeneous Helmholtz equation Pierre MARECHAL´ ,∗ Walter Cedric SIMO TAO LEE,† Faouzi TRIKI‡ May 7, 2021 Abstract The Cauchy problem for the inhomogeneous Helmholtz equation with non-uniform refraction index is considered. The ill-posedness of this problem is tackled by means of the variational form of mollification. This approach is proved to be consistent, and the proposed numerical simulations are quite promising. 1 Introduction Let V be a C3;1 bounded domain of R3 with boundary @V . For x0 @V , we denote by ν(x0) the unit normal vector to @V pointing outward V . Let Γ be a nonempty2 open subset of @V . We consider the Cauchy problem for the inhomogeneous Helmholtz equation ∆u(x) + k2η(x)u(x) = S(x); x V; (1) 0 0 0 2 @νu(x ) = f(x ); x Γ; (2) 2 u(x0) = g(x0); x0 Γ: (3) 2 1 arXiv:2105.02665v1 [math.AP] 6 May 2021 Here, u = u(x) is the unknown amplitude of the incident field, η L (Ω) is the refraction index, k is a positive wave number, S L2(Ω) is the source function,2 and f L2(Γ) and 2 2 ∗Institut de Math´ematiques universit´e Paul Sabatier, 31062 Toulouse, France. Email:
[email protected] †Institut de Math´ematiques universit´e Paul Sabatier, 31062 Toulouse, France. Email: wsimo-
[email protected] ‡Laboratoire Jean Kuntzmann, UMR CNRS 5224, Universit´eGrenoble-Alpes, 700 Avenue Centrale, 38401 Saint-Martin-d'H`eres,France. Email:
[email protected].