B. Haasdonk, and H. Burkhardt. Data analysis, machine learning and applications : proceedings of the 31st annual conference of the Gesellschaft für Klassifikation e.V, page 37-44. Berlin, Springer, (2007)
B. Haasdonk, and M. Ohlberger. Preprint / Albert-Ludwigs-Universität Freiburg, Mathematisches Institut Math. Inst., Freiburg, (2006)Extended version of an article submitted to M2AN.