Mario Bebendorf : H-matrix approximation of FE inverses for general elliptic operators
In this talk the efficient H-matrix approximation of FE stiffness matrices
in the case of uniformly elliptic operators with $L^\infty$ coefficients will be treated.
Unlike operators arising from boundary element methods for which the H-matrix theory
has been extensively developed the inverses of these operators do not benefit from the
smoothness of the kernel function. However, it will be shown that this does not affect the
existence of low-rank approximants. Emphasis will be laid on the influence of lower order terms
on the efficiency. Numerical examples will show that it is possible to generate the approximate
inverse with almost linear complexity.