With deep sadness, we bid farewell to a highly esteemed emeritus colleague who, over many decades, helped to shape the academic profile of our university — in particular within mathematics and computer science.

Hans Jörg STETTER was born on 8 April 1930 in Munich. After studying at TU Munich, he devoted his doctoral research (1956) to gas dynamics, specifically to hyperbolic partial differential equations. In the years that followed, he shifted his focus to the numerical analysis of ordinary differential equations and — especially after his appointment to the former Technische Hochschule Wien in 1965, where he established the university’s first digital computing center — became one of the leading figures in this emerging mathematical discipline.

His monograph Analysis of Discretization Methods for Ordinary Differential Equations (Springer, 1973) remains a standard reference to this day. Among his many innovative contributions are asymptotic error representations and defect correction methods for adaptive integration, which he developed and established as standard approaches.

In later years, Stetter turned to new topics, notably the — at the time still controversial — intersection of multivariate computer algebra and numerical analysis. As an emeritus professor, he published his second monograph, Numerical Polynomial Algebra (SIAM, 2004), after years of dedicated work beginning in 1998. His wide-ranging scientific interests were also reflected in numerous international collaborations, often pursued during research visits abroad.

He once aptly described his scientific attitude in an interview (2005):
“... in many cases up to now we see only the abstract final result, but not the way in which it was conceived ...”

As a university teacher, Hans Stetter shaped generations of students and colleagues. His teaching style was characterized by methodological clarity and the ambition to unite ideas, formal rigor, and intuition. Despite his fairness and collegiality, he set high standards — for himself and for his audience alike.

One of his characteristic sayings remains unforgettable:
“Error — that doesn’t mean that something was done wrongly ...”

Stetter was also deeply engaged in university policy. During his early years in Vienna, he was instrumental in establishing computer science as an independent and innovative discipline at TU Wien — actively and successfully advocating for this cause even at the federal level, when the national law governing technical studies was reformed in 1969.

With humor being his trademark, he once reflected on his pioneering role in the birth of computer science as an academic field in Austria:
“Austria is a hopeless case — but miracles have a positive expected value!”

To this day, the Faculty of Informatics remembers his crucial role as a trailblazer for “computational technology” at our university.
Even after his retirement, Hans Stetter remained closely connected to the Institute of Analysis and Scientific Computing and was a regular guest whenever current and former members of the institute gathered for events. We stayed in close contact — also in the years following the passing of his beloved wife Christine. Most recently, on April 25, 2025, we had the pleasure of celebrating his 95th birthday together with him, the Dean, and representatives of the Faculty of Informatics.

Our heartfelt condolences go to his family.

Winfried AUZINGER, Dirk PRAETORIUS, and Gabriela SCHRANZ-KIRLINGER
on behalf of the colleagues at the Institute of Analysis and Scientific Computing