Dual basis for the fully linear LL functions

The use of Buffa-Christiansen (BC) basis functions in the Calderon preconditioning of the electric field integral equation (EFIE) has been widely acknowledged during the recent years. The BC functions are dual functions of the lowest order (0.5) curl-conforming rotated Rao-Wilton-Glisson functions (RWG). The BC functions are defined as a linear combination of div-conforming RWG functions on a barycentrically refined mesh. Even though the number of elements in the refined mesh is six times larger, the computation time is decreased because the resulting matrix to be inverted is more well conditioned decreasing the number of iterations when solving the matrix equation iteratively.