In Memoriam: Jean Della Dora - SIGSAM

ACM Communications in Computer Algebra, Issue 168, Vol. 43, No. 2, June 2009
In Memoriam: Jean Della Dora
Jean Della Dora has left us . . .
Jean Della Dora retired last autumn, but he stayed very much in contact with the university and continued to
take an active role in its scientific activities and in the present discussions concerning the restructuration of the
university.
He was a pure product, from both a scientific and university point of view, of the direction begun at Grenoble
by Jean Kuntzman, and was one of the last and closest students of Noël Gastinel. His own contribution to the development
of applied mathematics and computer science at Grenoble in the last thirty years illustrate these relations.
After obtaining a bachelor’s degree in pure mathematics in 1967 and then an initial research diploma (‘diplôme
d’études approfondies’) in 1968 in number theory with Claude Chabauty, he decided to turn to applied mathematics
with Noël Gastinel.
He obtained a first position (‘assistant’) at the Université Joseph Fourier (then called Université Scientifique
Technologique et Médicale de Grenoble — USTMG) and in his first year obtained a master’s degree in mathematics
and fundamental applications and also began his initial research work. This was completed by a first thesis (‘thèse
de troisième cycle’) ‘On some eigenvalue finding algorithms’. These algorithms were viewed through the analysis of
certain subgroups of matrices.
In 1975 he was promoted ‘maître-assistant’ at USTMG and directed his work towards the approximation of complex
functions (Padé-Hermite, Hilbert spaces, . . . ). In 1980 he presented his second thesis (‘thèse d’Etat’) devoted
to this subject and also to a second topic, suggested by Bernard Malgrange, concerning singular complex differential
equations.
Even before presenting this thesis, Jean Della Dora’s interest in methods adapted to computer algebra led him
to codirect theses concerning this theme. Subsequently he directed around forty theses and ‘habilitations à diriger
des recherches’, in which he continued the transmission of his wide mathematical culture, handling subjects which
at the time seemed foreign to applied mathematics and anticipated the future explosion of computing. He acquired
this culture through a great interest in books: one could often see him in bookshops looking through works devoted
not only to mathematics, but also to other subjects such as science-fiction and the history of science. He was a great
defender of university libraries, both on a local and national level.
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Jean Della Dora
In 1980, when Jean Kuntzman left the position of director of LA 7 (Laboratoire Associé no. 7 CNRS) and
the laboratory was at its beginning, Jean Della Dora took over the responsibility of the numerical analysis team.
Up to this time, numerical analysts carefully avoided contact with large computers (and this, despite the incessant
encouragements of Noël Gastinel). With the arrival of personal computers, Jean Della Dora enabled the team to
obtain an IBM and then some Micrals and encouraged team members to consider the pleasures of programming. He
also encouraged and took part in interdisciplinary work groups which were developing at the time (automata theory,
control and automatics, spin glasses, . . . )
The rounds of restructuring (deconcentration and reconcentration) of laboratories, federations and so on were
beginning. The first of these resulted in 1983 in the separation of the IMAG (Institut de Mathématiques Appliquées
de Grenoble) into five laboratories and the creation of the new laboratory TIM3, in which Jean Della Dora took
an active part. He brought together workers in various fields: biology, medical science, circuit architecture, functional
security, numerical analysis, probability and statistics. Although still ‘maître-assistant’ (up till 1985, when he
became professor at the Institut Polytechnique de Grenoble — INPG), he was the natural choice for director of TIM3.
In a political context favorable to the development of new ideas in universities, Jean Della Della helped members
of the laboratory (finance, working conditions, . . . ) in the development of their individual projects (parallelism —
Michel Cosnard, medical computer science and modelling — Jacques Demongeot, . . . ). In a way similar to that of
Noël Gastinel (who left us in 1984), Jean saw himself modestly (sometimes too modestly) as an architect of ideas,
always helping in the realization of projects, without taking into account time and energy, and always with humor
and enthusiasm.
The meetings at the laboratory were always lively, although sometimes a little strained, being concerned with scientific
content and the development of projects. Jean was not particularly concerned with administrative questions,
but always respected those who had the responsibility for them. This activity at the laboratory led to its division
into three parts: Laboratoire de Modélisation et Calcul — LMC, Laboratoire TIMC et Laboratoire d’Informatique
de l’Ecole Normale Supérieure de Lyon.
Jean Della Dora left the position of director of the laboratory in 1991, but up till the end of his career, he was very
active in his research group. He also continued to play an important role in the scientific activities of the Institut de
Mathématiques Appliquées de Grenoble — IMAG, in the university calculation center (1991-96) and at the INPG.
He gave particular importance to the exchange of ideas, being convinced that a research worker must be free and
not always under the eye of a director or scientific advisor.
From 1980 onwards, Jean Della Dora became particularly interested in computer algebra and took part in its
development at Grenoble, in France (GRECO Computer Algebra), and internationally (CATHODE, CADE). Several
fields were and continue to be studied: the arithmetic of algebraic numbers, linear algebra, linear and non-linear differential
equations, difference equations, algebraic equations. The study of algebraic numbers led to the D5 paradigm,
named after Jean and his colleagues Dominique Duval and Claire Dicrescenzo, in which tedious computations and
case splits are deferred until they become easier, or are never needed. Jean also explored parallel computer algebra
and helped in the creation by his students of the first computer algebra system (PAC) to work on a parallel machine.
At the beginning this research was conducted in collaboration with the U. Louis Pasteur in Strasbourg (Jean-
Pierre Ramis) and the U. Libre de Bruxelles (Léon Brenig), then this collaboration was extended on the international
level: European project CATHODE (with two ‘work groups’), project CADE with the USA, Canadian collaboration
(Stephen Watt), research relations with Morocco. Jean played a major role in the research community of computer
algebra and differential equations. He was very innovative in directions of research, in particular in his comprehension
and vision of computer algebra.
His work and interest in exact linear algebra and computing and his legendary curiosity enabled Jean at an early
date to set into motion work on complexity and models of parallelism, which led to the formation of the team and
then the ‘Laboratoire Informatique et Distribution’.
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Jean Della Dora
Always being attentive to the development of subjects at the interface between mathematics and computing,
Jean Della Dora became naturally interested in the field of hybrid dynamical systems. There he saw the opportunity
to develop new algorithms combining symbolic and numerical aspects and to understand the regulation of genetic
mechanisms. Recently he became very interested in networks of dynamical systems and followed with great interest
the work in progress in his research team CASYS of the ‘Laboratoire Jean Kuntzman’.
Jean Della Dora taught a large range of subjects at different levels: numerical analysis, computer algebra, differential
equations, dynamical systems, hybrid systems, . . . . He developed courses for engineers, introducing algebraic
tools whose use in computer algebra and also in cryptography are now recognized. He also made available his experience
to colleagues both at the university and in high schools in the development of their courses.
More recently he devoted much of his attention to the teaching of mathematics to young people in difficulty. This
led him to consider new pedagogical questions.
His capacity to question ideas and to innovate, his extensive culture and his passion for research led to large
advances in the fields he studied. Jean Della Dora was able to communicate this passion to young research workers
and to set them on ways which were often new and innovative.
In the history of applied mathematics and computing at Grenoble, Jean Della Dora will have his place in that
due to creators and initiators. His enthusiasm and humor will not be forgotten.
His colleagues and friends at the ‘Laboratoire Jean Kuntzman’.
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