  The genetic cluster-exact approximation algorithm is an efficient method to
calculate ground states of EA spin glasses. The method can be used to study
ground-state landscapes by calculating many independent ground states for each
realization of the disorder. The algorithm is analyzed with respect to the
statistics of the ground states and the valleys of the energy landscape.
Furthermore, the distribution inside each valley is evaluated. It is shown that
the algorithm does not lead to a true T=0 thermodynamic distribution, i.e. each
ground state has not the same frequency of occurrence when performing many
runs. An extension of the technique is outlined, which guarantees that each
ground states occurs with the same probability.
