%0 Journal Article %T Fast integral equation methods for the modified Helmholtz equation %A Mary-Catherine Kropinski %A Bryan Quaife %J Mathematics %D 2010 %I arXiv %R 10.1016/j.jcp.2010.09.030 %X We present a collection of integral equation methods for the solution to the two-dimensional, modified Helmholtz equation, $u(\x) - \alpha^2 \Delta u(\x) = 0$, in bounded or unbounded multiply-connected domains. We consider both Dirichlet and Neumann problems. We derive well-conditioned Fredholm integral equations of the second kind, which are discretized using high-order, hybrid Gauss-trapezoid rules. Our fast multipole-based iterative solution procedure requires only O(N) or $O(N\log N)$ operations, where N is the number of nodes in the discretization of the boundary. We demonstrate the performance of the methods on several numerical examples. %U http://arxiv.org/abs/1006.0008v2