If you wish to have a personalized congratulations to Christiane Tammer published here, please send an email to Elisabeth Köbis (elisabeth [dot] kobis [at] ntnu [dot] no) or Markus Köbis (markus [dot] kobis [at] ntnu [dot] no).

Laudation by Alfred Göpfert

In the research work of mathematics (and not only there) it is important that we “see” something, that after reading, after a stimulating lecture, after remarks of an expert or maybe even after looking at a drawing we feel a hunch, an inkling, maybe even have an idea or vision what we could make out of a fact taken note of. I have seen many times in the past decades how jubilarian Christiane successfully seized such opportunities, combined them with her extensive and well-sorted knowledge of functional analysis and optimization, and then, often with colleagues and students and these scattered all over the world, obtained results.

When she was working in the eighties on the separation of two sets A, B in a topological vector space X, she came one day in a joyful mood and said that she suspected to be able to describe (under conditions) the separation by shifting one of the sets along a ray k emanating from the zero point in X. At first this was only a vision, but soon it turned out that with the shift a set of epigraphic type is formed, so that by infimum formation a functional can be formed which under conditions leads both to theorems about nonconvex separation and is suitable for scalarization in vector optimization and set-valued optimization. Through contributions of various authors, properties of the functional (as being f. i. convex, lsc., proper, monotone, finite-valued) have become more and more precise. Only recently, in a joint work with C. Zălinescu, she succeeded in showing Lipschitz properties of the functional, so that it is also suitable for obtaining optimality conditions. The honoree was also able to use the functional in proofs on extremality principles in the sense of Mordukhovich. B. S. Mordukhovich writes about her in page 100 of his 2018 monograph, "We also mention here important results on the so-called nonlinear separation that were initiated by Gerstewitz (Tammer) who was motivated by developing new scalarization techniques in vector optimization. Her idea was greatly elaborated and applied in many subsequent works"…Picked out from her extensive research work, perhaps a remark on preferences, i. e. order structures in general spaces, the basis of solution definitions. There are interesting applications of the functional especially w. r. to preferences concerning different concepts of robustness, I refer to her work with K. Klamroth, E. Köbis, A. Schöbel from 2017. Speaking on robustness there is a joint paper with E. Köbis of 2017 where both authors deal with robustness for uncertain vector optimization problems leading these problems to set-valued optimization problems with a variable domination structure, that means they look for cones C depending on the feasible points. Her research activities also include highly applied problems, and I refer here only to her results on location optimization.

A professor at a venerable university has even more obligations than research, I mention lectures, which are consistently well attended at her place; I mention contact with students, I know she is easily accessible; there are offices, she is vice dean; there is the German Association of Universities, she was chairperson in the state of Saxony-Anhalt for years and had thus "incidentally" all kinds of influence on university legislation in the state; furthermore she was (is) often co-author of books, also with me, and it was (and is) always a successful and very pleasant collaboration. She acquires so-called third-party funding, directs projects and now especially there is the Journal Optimization and she is Editor in Chief and finally, she has her doctoral and post-doctoral students; I wonder how she manages it all and so effectively? As an answer I come back to my thesis mentioned at the beginning: she "sees" connections and thinks quickly (and likes to do her job).

Laudation by Elisabeth Köbis

It is a great pleasure for me to write this laudation on Christiane Tammer, an outstanding scientist, mentor, and friend. I met Christiane for the first time in April 2007, when I attended her lecture on linear optimization. Not only did she spark my interest in mathematics in general and optimization in particular, she soon became my mentor and person I looked up to and consulted for guidance in any matters of science and life.

Christiane has provided 22 PhD students with her excellent counseling, leading them to each succeed in their own way. Some of her protegees thrived in academia, while others’ paths led them to find their way in industry. One of the unifying characteristics they all have in common is that they all have benefited from Christiane’s thorough, personal advising, which laid the foundation of their professional life.

I find it outstanding how Christiane manages to fulfill her many roles with such great success, involvement, and humanity. As Editor-in-Chief of the journal Optimization, she constantly is engaged with upholding and enhancing the quality and outreach of the journal. This is not only visible in the increasing impact factor of the journal, but also in the contentment and gratitude of authors, editors, and reviewers. Her many activities in Editorial Boards of various journals also need to be mentioned, among others, at the Journal of Nonlinear and Variational Analysis, Journal of Applied and Numerical Optimization, Journal of Optimization Theory and Applications, Mathematical Inverse Problems, Minimax Theory and its Applications, Investigación Operacional, Applied Analysis and Optimization, and Vietnam Journal of Mathematics. She also serves as one of the Editors-in-Chief at Applied Set-Valued Analysis and Optimization. It is important to mention here that she especially takes great effort in supporting newly founded journals on their way to become successful and established in the optimization community.

Her research work is highly appraised world-wide. She co-authored five monographs, which present fundamental results together with various of her many contributions in a lucid style.

As Professor at the Martin-Luther-University in Halle-Wittenberg, she has been or currently is, amongst others, vice dean for research, member of the examination committee, chairperson of the PhD panel, member of the panel of the Stiftung Mathematik / Theoretische Physik, organizing the monthly colloquium of the institute, organizing the correspondence circle (a project for highschool students interested in mathematics), and acting as liaison lecturer with the Rosa Luxemburg Stiftung. As chairperson of the regional association Saxony-Anhalt of the German Association of University Professors and Lecturers, Christiane, again with great dedication, represented the professional interests of university teachers in opposition to state and society. It is incredible how she manages all her commitments with the same, strong and ever growing involvement and energy.

She has been a mentor not only for her students, but also for young researchers from around the world that she met, for example, at conferences or via colleagues. Always open and helpful to anyone, it is no surprise that she is well-liked among researchers worldwide. Anyone working with her will testify what a delight she brings to any collaboration.

Christiane, together with her colleagues from Freiberg, annually organizes a workshop on set and vector optimization in the historic setting of the university library in Wittenberg, which presents a pleasant opportunity for the younger researchers to present their results and discuss them in a friendly surrounding.

Christiane’s lectures, both at the university as well as research lectures at conferences and workshops, are always a delight to listen to and give much inspiration.

Most importantly, Christiane is known as a kind-hearted, generous person with a dedication for humanity. I am very thankful to her for all that she has taught me in the last 14 years, and I am looking forward the next ones. It is an absolute pleasure for me to celebrate this colloquium dedicated to her 65th birthday with Christiane and her friends.

 Elisabeth Köbis, Christiane Tammer and Thanh Tam Le at a conference in Hokkaido, Japan

Laudation by Renate Patz

A life for mathematics and for a well together in working and living. Laudatio for Christiane Tammer dedicated to her 65th birthday.

It is a great pleasure for me to praise Christiane Tammer as an outstanding and amazing woman. There are the two sides of the same coin: Her life for the science and especially for mathematics and on the other side her human side, her personal qualities, her life towards a better way of working and living together.

She is known worldwide for her excellent work on the field of mathematical optimization. It is also truly important to her to contribute with the help of research in optimization to solve real problems. We experienced this when we had been worked in the 1990s at the University of Applied Sciences Merseburg on a number of projects on the field of urban and regional planning. It has to be said that it was a very special situation in East Germany at that time, resulting from the reunion of the two German states, the merging of different societies. There had been fundamental changes in all structures of society, changes in the economy, policy, education, science, in the life and work of the people. The former Technical University of Leuna-Merseburg – where Christiane studied and received her doctoral degree – was shut down in 1993. On the same campus a new university was founded in 1992, the University of Applied Sciences Merseburg in accordance with the West German higher education system. Closeness of application and a close connection to the regional economy are characteristic of these universities. The ambition of the University of Applied Sciences Merseburg was from the beginning that it should be a university with a special focus on applied research.

In the early 1990s I worked in the project group Technology Assessment. We investigated different change processes during this special time. With a project for investigating the acceptance of changes of green and open spaces of the city of Halle my activities began at the University of Applied Sciences Merseburg. There were many questions how to manage processes in the urban development in the new context. In particular, one of the problems in urban planning was the traffic problem, due to the extremely high increase of motorized individual traffic in an extremely short time period. Missing of parking lots was part of the traffic problem. One question was: It is better to reduce green areas for parking lots or to look for a suitable location for a new car park?

Christiane noted, that this is a typical example of a location problem and she suggested the multicriteria approach to describe the change and decision process as a multicriteria optimization problem. This makes it possible to consider different alternatives resulting from different criteria and weights. The corresponding algorithms developed by Christiane are used successfully to solve location problems and further problems in planning practices. It was possible to propose a way to support town planners in making decisions. The project initiator and planners recognised, that the multicriteria approach is practical way to qualify the discussion process with all involved actors with their special, usually competing interests to find the best solution. At the same time, this was also a learning process, a challenge for understanding between planners and mathematicians. For example, to transform a planning problem into a mathematical model or, on the other side, to consider real-world conditions of the concrete town in the mathematical model. Christiane was ever a good and understanding partner. Stimulated by Christiane the solution procedure was later combined with Geographical Information Systems (GIS), which were developed in cooperation with the company SCC GmbH Merseburg. With this it was possible to visualize the solutions in the map.

Further applications have been examined. Such an example was resulting from the rehabilitation and recultivation of nearly all former open-cast mines. One of the largest and well known (because of the fossil finds) is the Geiseltal not far away from city of Halle. Like most of the Central Germany’s open-cast mines the Geiseltal open-cast mine was closed in the 1990s. The aim of redevelopment of former coal-mining areas was to create a solid and high-grade varied usable landscape. This means that there are created completely new landscapes by humans. A number of interests for the use of future land need to be taken into account. Where should be locations and areas for housing, working, leisure, nature etc. so that recultivation leads to an optimal development in the sense of a sustainable development of the region? Which facilities of former mining should maintain and for which purposes they could be used? Is a former machinery hall of a disused briquette factory in the Geiseltal a suitable location for a new cultural and tourist centre? This is exactly the aim of a non-profit association, to converse a former building of mining to an industrial monument. The study as a multicriteria location problem showed under what conditions this location is good. For the association it was a confirmation that it is worth fighting with commitment to preserve things which were left to us by past generations and times and that there are people like Christiane who are on the point of helping.

The collaboration with Christiane has been a very good experience for my later activity as coordinator of research and knowledge transfer at the young University of Applied Sciences Merseburg. These are experiences to know what is relevant for the management of successful research and development, how young researchers are to be promoted etc. As one of the first ones Annette Henn has concluded in 2004 successfully a cooperative doctorate procedure in the Economic Sciences Department. She investigated the management of land use under aspects of nature protection, social concerns and economic efficiency. She received important informations from Christiane for the mathematical modelling and investigation of decision-making processes containing a number of criteria and in cases of differing interests. Another good example of the influence of Christiane is that she knows how important it is in science to make the results public. She offers us the opportunity to present our results and experiences of the application of location optimization and methods of decision support on national and international conferences.

Well, that is all a long time ago, but linked with sustainable effects and many wonderful memories. Christiane is an extraordinary and amazing woman. She paved the way for many people and projects through her profoundly and untiring work in science. She stands for deep knowledge and high degree of various interests, passion on art and culture, nature and gardening, sports activities such as swimming, skiing, hiking or biking. During the lengthy time - since the 1970s we know each other – it has developed a close friendship. I have seen how important to her are work and mathematics just like family and friends, how good and loving she was to her parents and to her son. She is also known for her respect, steady helpfulness, compassion, especially for those people who are disadvantaged.

Christiane is herself the proof of the fact that mathematics is not just an abstract or vague theory but rather is of great practical benefit, and how much mathematicians can achieve for humans being. Her understanding and support for voluntary work is encouragement for their doing. On this way these initiatives get acknowledgement and appreciation by important persons like Christiane. Our society needs urgently more motivated persons of integrity like Christiane.

Dear Christiane, thank you so much for all, for your dedication and friendship. I wish you all the best for upcoming time, health, optimism, energy, always a good life.

Many thanks also to the organizers of the ICVANO conference, it is a wonderful occasion to praise Christiane.

Renate Patz
July 2021

2021-07-11, Elisabeth Anna Sophia Köbis