Computing the twisted $L^2$-Euler characteristic

Abstract

We present an algorithm that computes Friedl and Lück's twisted $L^2$-Euler characteristic for a suitable regular CW complex, employing Oki's matrix expansion algorithm to indirectly evaluate the Dieudonné determinant. The algorithm needs to run for an extremely long time to certify its outputs, but a truncated, human-assisted version produces very good results in many cases, such as hyperbolic link complements, closed census 3-manifolds, free-by-cyclic groups, and higher-dimensional examples, such as the fiber of the Ratcliffe-Tschantz manifold.

48 pages, 5 figures. Replaced to match the journal version. An implementation of the algorithm can be found on GitHub at https://github.com/floatingpoint-754/twisted-l2-characteristic