Approximation of integral operators by H2-matrices with adaptive bases

H-2-matrices can be used to construct efficient approximations of discretized integral operators. The H-2-matrix approximation can be constructed efficiently by interpolation, Taylor or multipole expansion of the integral kernel function, but the resulting representation requires a large amount of storage. In order to improve the efficiency, local Schur decompositions can be used to eliminate redundant functions from an original approximation, which leads to a significant reduction of storage requirements and algorithmic complexity.