2 Martin H. Gutknecht is a professor and senior scientist at ETH Zurich. He was also Scientific Director of the Swiss Center for Scientific Computing (CSCS/SCSC). Numerical Analysis in Zurich – 50 Years Ago Surely, applied mathematics originated in ancient gathering of this sort ever – as an opportunity to times and slowly matured through the centuries, recall some of the local contributions. We focus on but it started to blossom colorfully only when those in numerical analysis and scientific comput- electronic computers became available in the late ing, but we will also touch computers, computer 1940s and early 1950s. This was the gold miner’s languages, and compilers. time of computer builders and numerical analysts. Responsible for establishing (electronic) The venue was not the far west of the United scientific computing in Switzerland was primarily States, but rather some places in its eastern part, Eduard Stiefel (1909–1978): he took the initiative, such as Boston, Princeton, Philadelphia, and New raised the money, hired the right people, directed York, and also places in Europe, most notably, the projects, and, last but not least, made his own Manchester, Amsterdam, and Zurich. Only long lasting contributions to pure and applied math- after these projects had begun did it become ematics. Stiefel got his Dr. sc. math. from ETH in known that the electronic computer had been 1935 with a dissertation on Richtungsfelder und invented earlier by clever individuals: 1937–1939 Fernparallelismus in n-dimensionalen Mannig- by John V. Atanasoff and his gradute student faltigkeiten written under the famous Heinz Hopf. Clifford Berry at Iowa State College, Ames, Iowa, It culminated in the introduction of the Stiefel and, independently, 1935–1941 by Konrad Zuse in (-Whitney) classes, certain characteristic classes Berlin. We take the Sixth International Congress of associated with real vector bundles. Eduard Stiefel Industrial and Applied Mathematics – the biggest left further traces in pure mathematics with the Figure 1 The South Seas island of ERMETHIA Stiefel manifold and, later, in 1942, with the Stiefel diagram related to Lie groups and crystallographic groups. Decades later he would time and again capitalize on this knowledge by applying it to various problems in applied mathematics. InWWII, Stiefel spent much time in the army, where he reached the rank of a colonel, command- ing the artillery weather services. That must have whetted his appetite for numerical computations. Moreover, soon after the war he must have heard of projects to build electronic computers in other countries, and he quickly started an initiative for establishing an Institute for Applied Mathematics at ETH. Its prime aim would be to build an electronic computer – there were none for sale then – and to find out how to use it. There were no operating systems yet, no compilers, no program- ming languages, and little algorithmic thinking. As it turned out, Stiefel’s institute, which was Figure 2 Eduard Stiefel, the chief, who had an interest in fishing founded officially on January 1, 1948, became one of the few places worldwide that made fundamen- relays. It was, however, error-prone, but useful as tal contributions to all these areas within 10 years. a prototype to get support for his next project. The After establishing the institute, Stiefel soon Z3 was completed in 1941 and was a fully opera- hired two assistants: a young mathematician tional programmable computer based on the relay named Heinz Rutishauser (1918–1970) and a technology: 600 relays were used for the CPU, young electrical engineer named Ambros Speiser 1400 for the memory. A replica is now on display (1922–2003). Rutishauser had been working as in the German Museum in Munich. Finally, in a high-school teacher and was about to finish his 1942–1945, Zuse built the more powerful Z4. dissertation on a topic in complex analysis. Speiser In the last month of the war, he was able to flee the (1922–2003) was just about to get his diploma. capital with his Z4 packed up in boxes and to Next, Stiefel went for five months (from October retreat to the secluded village of Hinterstein, close 18, 1948, to March 12, 1949) on a fact finding to the Austrian border. Once the end-of-war mission to Amsterdam and the United States. turmoil had cooled down, Zuse moved to the He visited several computer building projects and better accessible Hopferau, where, in 1946–1949, some colleagues who worked on algorithms for he completed the Z4 in the former flour storage scientific computing. He also organized for each of room of a bakery. After inspecting the machine, his two assistants to spend the whole year of 1949 Stiefel leased the Z4 for CHF 30’000 for five years. in the US. Each of them could stay half the year It was installed at ETH in August 1950, often ran with Howard Aiken at Harvard University and the day and night, and proved very reliable, except for other half with John von Neumann at Princeton. the memory (64 32-bit numbers), which was still What a generous boss! And what a clever move for mechanical. The technical details have been know-how acquisition! Fostering these two young reported in many newspaper and journal articles, researchers payed off well – as it generally does. see, e.g., [2], [17], [5], and the references listed in When Stiefel returned in Spring 1949 he had to there. Some new features were added in Zurich, anticipate that designing and constructing an e.g., the treatment of conditional branches. electronic computer in Zurich would take several Despite the Z4, designing a more powerful years, and during this time work on numerical electronic computer to be called ERMETH algorithms would be limited by the impossibility (Elektronische Rechenmaschine der ETH) was of testing them. He was more than happy to learn still the main target of Stiefel’s quickly growing one day that Konrad Zuse who lived in the small institute. Responsible for this task was Ambros Bavarian village Hopferau offered to lease him an Speiser, in the meantime the technical director of operational digital electromechanical computer. a group of five engineers and three mechanics. Konrad Zuse was a real inventor. In 1935–1945 he But reportedly, Rutishauser’s ingenious views also designed a series of four digital computers with had a great influence on the design. Among the binary floating-point representation in his parents’ traces of their work are the two reports [16], [11], apartment in Berlin: while the Z1 was still fully the latter being Rutishauser’s habilitation thesis mechanical, the Z2 of 1940 had already an describing what we would call now a compiler. arithmetic unit assembled from electromagnetic Ultimately, the ERMETH started running in July 4 center head Article Figure 3 Ambros Speiser, who was always trying to maintain the site Figure 4 Heinz Rutishauser, fond of music, shown below a broken in order chain, in German Kettenbruch, i.e., continued fraction 1956 and remained operational till 1963. Its most working on the theory of a clever improvement impressive part was a large magnetic drum that of the Gauss-Seidel method. Young’s successive could store 10’000 floatingpoint numbers in overrelaxation (SOR) method proved to be very a 16-decimal representation with an 11-decimal efficient for many symmetric positive definite mantissa. For further details on the ERMETH see (spd) problems (and a few others). Stiefel also [10] and the references given there. knew of a number of other, competitive, “relaxa- Running the Z4 and at the same time building tion” methods that were equally simple to apply the ERMETH was a lot of hard work for the team and did not use a matrix splitting, but – like SOR – of the institute, work often carried out day and required choosing certain parameters. The best night. The excellent team spirit is reflected in our such method is known as Chebyshev iteration as it illustrations that show the mystic South Seas island makes use of Chebyshev polynomials. But Stiefel of ERMETHIA and the four most prominent team was looking for a better method that automatically members as its inhabitants. The drawings were adapts to each matrix and to the initial approxima- sketched by Alfred Schai in coal on large sheets of tion of the solution. He discovered it in 1951: an paper around 1956, but only photographs survived iterative method that delivers for spd problems in the years. Schai was an electrical engineer of the every step an optimal approximation of the team, who later, 1964 –1989, was director of the solution and constructs it with an update process well equipped Computer Center of ETH Zurich. based on simple 2-term recurrences. He called it The availability of the Z4 allowed Stiefel and his the n-step method, as it delivers the exact solution collaborators to explore numerical methods on it. of a linear n-byn system in at most n steps. He first They also attacked real applications from civil mentioned it in a paper submitted in July 1951, engineering (dams, plates), quantum chemistry in which he reviewed various approaches to the (eigenvalues), and airplane design (deformation of iterative solution of linear systems [18]. wings). Most of the textbook methods of this area In the same month he travelled to the United originated from the time when “computers” were States for a second, even longer visit (from July still human beings. Some of these methods were 1951 to February 1952), this time to the Institute suitable for programmable electronic computers, for Numerical Analysis (INA) of the National others proved inappropriate or inefficient. The Bureau of Standards, which was located at UCLA strong limitations regarding memory and program in Los Angeles.