At the 18th International Conference on Operational Research KOI 2020, September 23-25, Amadria Park, Sibenik, Croatia a special session devoted to Professor Emeritus Sanjo Zlobec, on the occasion of his 80th birthday, was organized by Luka Neralić, Krunoslav Puljić and Vedran Kojić. Details on attendants, who were invited from the list suggested by Sanjo Zlobec, and their presentations can be found below. Before that some facts on Sanjo Zlobec from his Curriculum Vitae are presented. On Sanjo Zlobec you can see also in: L. Neralić, "Sanjo Zlobec", Istaknuti hrvatski znanstvenici u Americi, Drugi dio, Distinguished Croatian Scientists in America, Part Two, Urednik (Editor) Janko Herak, Hrvatsko-američko drustvo, Hrvatska matica iseljenika i Matica Hrvatska, Zagreb, 1999, 141-157.

Professor Emeritus Sanjo Zlobec was born in November of 1940 in Brezicani near Banja Luka. Sanjo attended an elementary and high school in Zagreb. He graduated at the Department of Mathematics, Faculty of Science, University of Zagreb, in 1965 and started his university career in the same department. He was awarded a master's degree in 1967 with the thesis "Matrix Iterative Analysis in Finite Dimensional Spaces and Applications" under the supervision of Professor S. Kurepa. In 1968 he was awarded a Fulbright grant and went to the Department of Engineering Sciences, Northwestern University, Evanston, Illinois, USA to study with Professor Adi Ben Israel. There he was awarded a Ph.D. with the thesis "Contributions to Mathematical Programming and Generalized Inversion" in 1970.  

At the Department of Mathematics and Statistics, McGill University, Montreal, Canada, he was Assistant Professor (1970-1976), Associate Professor (1976-1984), Professor (1985-2005) and Professor Emeritus since 2009. During a leave of absence he spent the winter semester of 1970/71 teaching at the Department of Mathematics, University of Zagreb. As Visiting Scientist he was on sabbatical leave in 1978/79 at the Department of Mathematical Sciences, University of Delaware, Newark, Delaware, USA, at the Department of Computer Sciences, Technion - Israel Institute of Technology, Haifa, Israel, and at the National Research Institute for Mathematical Sciences, Pretoria, South Africa (where he also spent part of 1985/86). In 1985/86 and 1993/94 he was Visiting Professor at the University of the Witwatersrand, Johannesburg and University of Zagreb. At the University of Witwatersrand he was founder of the branch of Almae Matris Croaticae Alumni (AMCA).  

His research activities started with generalized inverses of matrices and linear operators, then moved to optimality conditions in various mathematical programming areas, including parametric programming, and stability of mathematical models in applied mathematics. He presented more than 100 invited lectures at international conferences in mathematics, operations research, mathematical programming, parametric programming and related topics, at universities around the world. Under his supervision 17 students received master's degrees and 5 students received Ph.D.s. He was organizer or/and chairman of sessions at more than 30 international symposia all over the world. Professor Zlobec is one of the editors of "CIT" and a member of the editorial boards of several journals, including "Optimization," "Questiones Mathematicae," "Glasnik Matematički", "Mathematical Communications," and "International Journal of Optimization: Theory, Methods and Applications". The list of Professor Zlobec's publications contains about 100 papers in professional journals, proceedings and encyclopedias on mathematics and applied mathematics, in particular operations research and optimization. He is also the author of the research monograph "Stable Parametric Programming", Kluwer, 2001, which is very important and has a big influence in that area.  

Since 2010, when sessions devoted to Professor Zlobec in occasion of his 70th birthday were organized by L. Neralić at the 17th International Conference on Operational Research in Split, he continued to do research and publishing. After that he published several new papers in journals, technical reports and conference papers on different topics. Let us mention a few of them, which seems to be most important: [1] Zlobec, S. (2011a). Note on the Fermat extreme value theorem, Communications on Applied Nonlinear Analysis 18 (3), 99-103.; [2] Zlobec, S. (2011b). Equivalent formulation of the gradient, Journal of Global Optimization 50 (3) , 549-553.; [3] Zlobec, S. (2014a). Modelling with twice continuously differentiable functions, Croatian Operational Research Review, CRORR 5, 1-13.; [4] Zlobec, S. (2014b). Separation property of continuously differentiable functions, Mathematical Communications 19 (1), 57-64.; [5] Zlobec, S. (2018). Geometry of local optima, Pure and Applied Functional Analysis 3 (4) 743-751.  

In the session devoted to Sanjo's 80th birthday at KOI 2020 in Sibenik there were 9 presentations, one live and eight online. Here are the names of the presenters and the titles of presented papers (in order of presentation): 1. Dragan Jukić and Tomislav Marosević, Josip Juraj Strossmayer University of Osijek, Osijek, Croatia. "Least squares fitting problem for the power-law regression with a location parameter" (live).; 2. Masoud Asgharian, McGill University, Montreal, Canada. "Stochastic ranking and dominance in DEA".; 3. Richard E. Wendell, University of Pittsburgh, Pittsburgh, PA, USA. "The dangers in using earned duration and other earned value metrics to measure a project's schedule".; 4. Goran Lesaja, Georgia Southern University, Statesboro, USA. "A full-Newton step interior-point method for monotone weighted linear complementarity problems".; 5. Adi Ben Israel, Rutgers Business School, Livingstone Campus, Piscataway, NJ, USA. "Every iteration, away from its fixed points, is Newton".; 6. James F. Peters, University of Manitoba, Winnipeg, Canada. "Amiable fixed sets in CW spaces - Brower fixed point theorem extension and day amenable finite group". ; 7. Professor Abraham Berman, Technion - Israel Institute of Technology, Haifa, Israel. "C(O)P matrices and optimization".; 8. Muhammad Adil Khan, University of Peshawar, Khyber Pakhtunkhwa, Peshawar, Pakistan. "Majorization theorems for strongly convex functions".; 9. Shashi Kant Mishra, Banaras Hindu University, Varanasi, Uttar Pradesh, India. "q-BFGS algorithm for unconstrained optimization problems".  

A special issue of the Central European Journal of Operations Research (CEJOR) will contain papers presented at the KOI 2020 in Sibenik, which will be submitted and accepted for publication, including papers presented in the session devoted to Professor Zlobec. Guest editors of the special issue are M. Asgharian, Z. Lukač, L. Neralić and R. E. Wendell.  

Professor Zlobec's connections with Croatia are numerous and permanent. He has given many seminars at the University of Zagreb, both at the Faculty of Economics and the Department of Mathematics. He is one of the founders of the Croatian Operational Research Society (CRORS), which was established in 1992. He was on the executive committee of the 6th International Conference on Parametric Optimization and Related Topics, Dubrovnik, 1999. He has been an investigator in the project "Mathematical Methods and Models of Operational Research in Economics and Decision Making," sponsored by the Ministry of Science, Education and Sport, at the Faculty of Economics and Business, University of Zagreb, since 2007. He has also been a reviewer of graduate programs with the National Foundation for Science, Higher Education and Technological Development of the Republic of Croatia. At the 17th International Conference on Operational Research KOI 2018, September 26-28, 2018, Zadar, Croatia, Sanjo got the Award for Special Contribution to Croatian Operational Research Society (CRORS) in recognition of his distinguished service to CRORS and to the profession of operations research. Sanjo's daughter Inti accepted the award on his behalf and presented Sanjo's paper "Thirty Millennia of Operation Research".  

Luka Neralić, Professor Emeritus at the Faculty of Economics and Business (EF), University of Zagreb Zagreb,
February 15, 2021