In this talk we present a multigrid second order accurate method to solve Elliptic equations with discontinuous coefficients on an arbitrary interface. Second order accuracy for the gradient derivative is obtained as well. The method is based on the Ghost Fluid Method, making use of ghost points on which the value is defined by suitable interface conditions. The multi-domain formulation is adopted, where the problem is split in two sub-problems and interface conditions will be enforced to close the problem. Interface conditions are relaxed together with the internal equations, leading to an iterative method on all the set of grid values (inside points and ghost points). A multigrid approach with a suitable definition of the restriction operator is provided. The restriction of the defect is performed separately for both sub-problems, providing a convergence factor close to the one measured in the case of smooth coefficient and independent on the magnitude of the jump in the coefficient. Numerical tests will confirm the second order accuracy.
[1] A. Coco and G. Russo. A fictitious time method for the solution of Poisson equation in an arbitrary domain embedded in a square grid. Journal of Computation Physics. Under revision.
[2] A. Coco and G. Russo. Multigrid approach for Poisson's equation with mixed boundary condition in an arbitrary domain. Submitted. Preprint available in http://arxiv.org/pdf/1111.0983.
[3] A. Coco and G. Russo. Second order multigrid methods for elliptic problems with discontinuous coefficients on an arbitrary interface, I: one dimensional problems. Numerical Mathematics: Theory, Methods and Applications. In press. Pre-print available in http://arxiv.org/pdf/1111.1167.
[4] A. Coco, F. Gibou, and G. Russo. Adaptive solvers for Poisson problems with discontinuous coefficients on Cartesian grids. Submitted.