Hans-Bernd Knoop

Heiner Gonska

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REVUE D’ANALYSE NUMÉRIQUE ET DE THÉORIE DE L’APPROXIMATIONRev. Anal. Numér. Théor. Approx., vol. 30 (2001) no. 2, pp. 125–126ictp.acad.ro/jnaatON THE 60th BIRTHDAY OF PROFESSOR WERNER HAUSSMANNThis issue of ”Revue d’Analyse Numérique et de Théorie de l’Approxima-tion” is dedicated to Professor Werner Haußmann who will celebrate his 60thbirthday on November 12, 2001.Werner Haußmann was born in Nürtingen in the Southwestern part of Ger-many. After finishing high school (the German ”Gymnasium”) there in 1961,he studied mathematics and physics at Eberhard Karls University in Tübingenuntil 1966. His original aim had been to become a school teacher. However,he finished the university with the diploma in mathematics and a thesis onChebyshev approximation by exponential functions. These studies broughthim in touch with several prominent members of the famous Tübingen schoolof mathematics, and with Hartmut Ehlich (his diploma advisor) and KarlZeller, in particular.In 1966 he became assistant to Professor Ehlich who had moved fromTübingen to the newly founded Ruhr University at Bochum. Haußmann fin-ished his doctoral degree in 1969 with Ehlich and a thesis on Hermite interpo-lation in several variables. His ”Habilitationsschrift” dating from 1971 dealtwith the theory of spline systems. The latter work enabled him to becomelecturer (”Dozent”) in 1971 and associate professor (”Wissenschaftlicher Ratund Professor”) in 1972, both at Bochum. Already before his ”Habilitation”he had started to gather a number of gifted students around him, giving themguidance during the preparation of their diploma theses.In 1975 he accepted an offer for a full professorship at the University ofDuisburg, now being Gerhard Mercator University. At Duisburg he foundedthe well–known group in applied analysis, and has also been serving the de-partment and the university in many administrative duties until the presentday.On July 27, 1978 Werner Haußmann married Dr. Ilse Becker, a formerassistant in the geometric algebra group at Duisburg. After getting settled inMülheim on the Ruhr where they have been living since then, three childrenwere born: Ute, Ulrike, and Peter.In a natural and obvious way, the scientific activities of Haußmann can bedivided into several streams, some of them running in parallel now.As was already mentioned, his individual research started in (multivariate)interpolation and approximation by polynomials and splines. These fieldsremained in the focus of his interest until the late 70’s.At about that time he started a most fruitful collaboration with Karl Zeller(a direct scientific descendant of Karl Weierstrass) which continued over al-most two decades. During this period in some 20 joint articles (several of126 On the 60th Birthday of Professor Werner Haußmann 2them written in collaboration with further authors) Haußmann and Zeller in-vestigated a wide variety of topics in numerical analysis, approximation andpotential theory, including quadrature formulae, multivariate approximationand interpolation methods of various types, as well as questions in harmonicapproximation.It was around 1983, when harmonic approximation started to catch Hauß-mann’s interest most intensively. His first paper in that field was writtenjointly with the late M. Goldstein and K. Jetter, published in 1984 and dealtwith best harmonic L1 approximation to subharmonic functions. Later manyfurther papers on the subject followed in which – in addition to the above men-tioned authors – joint research with D. Armitage, St. Gardiner, O. Kounchev,L. Rogge, and L. Wehrend was presented. Research in this field has been goingon until present, one of the most recent contributions dealing with incompletelattice sets that control the behaviour of entire harmonic functions.Towards the end of the 80’s Werner Haußmann also became actively in-volved in attracting the international approximation community to the Ruhrarea, that is, the former mostly industrial part of West Germany stretchingalong the river Ruhr from Dortmund in the East to Duisburg in the West. Sofar, the outcome of these activities have been four international meetings onmultivariate approximation and interpolation, one at Duisburg in 1989 andthree subsequent ones at Witten–Bommerholz (1996, 1998, 2000). All of themhave drawn a most distinguished audience and significantly contributed to animprovement of the area’s reputation as a center of research and development.In addition he was also one of the organizers of a conference at the Mathe-matical Research Institute at Oberwolfach (1988) and of a NATO advancedresearch workshop in Hanstholm/Denmark (1991).In about 1994 Haußmann started a most productive collaboration with sev-eral members of the Bulgarian school of approximation, including academicianB. Bojanov. This activity has also continued until present and has triggeredmany valuable contacts between the Bulgarians and other members of thedepartment at Duisburg.In summary, it should be mentioned that all the scientific initiatives (whichwe were only able to roughly sketch in the above) lead to some 60 papersauthored by Werner Haußmann and his co–authors, and that 12 doctoralstudents plus their descendants profited from his scientific leadership.Four of his former Ph.D. students are professors at different German uni-versities now, and the authors of this article are two of them. We are mostpositive to speak on behalf of all of Professor Haußmann’s students when ex-pressing our best wishes for the future, in particular for continuing success inhis various professional activities and a life full of health and happiness.Heiner Gonska and Hans-Bernd Knoop

On the 60th Birthday of Professor Werner Haussman

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On the 60th Birthday of Professor Werner Haussman

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