@misc{callies_a_multigrid_1990, 
author={Callies, U.,Eppel, D. P.},
title={A multigrid approach to optimizing the initial values of hyperbolic model equations},
year={1990},
howpublished = {conference lecture: Bonn (D); 1.-4. Oktober 1990},
note = {Online available at: \url{} (DOI). Callies, U.; Eppel, D.: A multigrid approach to optimizing the initial values of hyperbolic model equations. Third European Conference on Multigrid Methods. Bonn (D), 1990.}}