@misc{callies_on_the_1994, 
author={Callies, U.,Eppel, D. P.},
title={On the eigenvalues of the cost functions Hessian when fitting linear hyperbolic equations to data},
year={1994},
howpublished = {conference lecture: Grenoble (F); 25.-29.04.1994},
note = {Online available at: \url{} (DOI). Callies, U.; Eppel, D.: On the eigenvalues of the cost functions Hessian when fitting linear hyperbolic equations to data. XIX General Assembly of the European Geophysical Society. Grenoble (F), 1994.}}