Events

We devise a testing framework to rank proxy-based influence maximisation algorithms. Earlier works compare these algorithms by calculating their top choices on a given network, then checking which set fares better in a diffusion simulation. In real-life applications, however, the top choices of these algorithms might be unaccessible for various reasons. Consequently, we have to choose our spreaders from a different set that might not contain any highly ranked agents at all. There is no guarantee that a proxy that is better at predicting the performance of the most popular agents will be equally successful for an arbitrary group of individuals. This calls for a systematic test, and in this paper, we provide one with the help of a novel statistical method, the Sum of Ranking Differences. For demonstration, we use the real-life social network, iWiW and a classical diffusion model, the Linear Threshold. The final ranking of the proxies is remarkably different from what we obtain by examining the performance of their top choices. The results highlight that the standard test alone is an inadequate predictor of performance and SRD should be a necessary, if not the primary tool for ranking proxies

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In a cooperative game when the problem of computing the minimum excess coalition for a given allocation can be formulated as a dynamic program we show that the nucleolus can be computed in time polynomial in the size of the dynamic program. This gives a general technique for designing efficient algorithms for computing the nucleolus of a cooperative game. This technique is inspired by a recent result of Pashkovich on weighted voting games. However, our technique significantly extends beyond the capabilities of previous work. We demonstrate this by applying it to give an algorithm for computing the nucleolus of b-matching games in polynomial time on graphs of bounded treewidt

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We find that the interconnectedness of global gas markets through abundant LNG import capacity both in Europe and other regions – namely in Asia – allows for adjustments of global trade patterns that mitigatethe consequences of regional disturbances. Neither Chinese nor German subsidies on regasification terminals nor moderate financial support of US LNG exports affect aggregate EU consumption levels in a significant way. Only a Russian boycott or large subsidieson US LNG exports have a discernable effect. In any year, compared to the Base Case, EU consumption varies not more than between -5% and +3%, and average prices by -5% to +10% only.

If you wish to receive a link for the zoom meeting on the day of the event, please send an email to Tamás Solymosi (tamas dot solymosi at uni dash corvinus dot hu)

Our talk will have two parts. First, we give an introduction to optimisation in two-sided matching markets by giving details also on practical results in different applications, such as the Hungarian university admission scheme. Then we present a novel application for allocating voluntary mentors to students. After the closure of the schools in Hungary from March 2020 due to the pandemic, many students were left at home with no or not enough parental help for studying, and, in the meantime some people had more free time and willingness to help others in need during the lockdown. In this paper we describe the optimisation aspects of a joint NGO project for allocating voluntary mentors to students using a web-based coordination mechanism. Our goal has been to form optimal pairs and study groups by taking into the preferences and the constraints of the participants. We present the optimisation concept, the integer programming techniques used, and some simulation results conducted on real and generated datasets.

If you wish to receive a link for the zoom meeting on the day of the event, please send an email to Tamás Solymosi (tamas dot solymosi at uni dash corvinus dot hu)

In an information graph situation, some agents that are connected by an undirected graph can share with no cost some information or technology that can also be obtained from a source. If an agent is not connected to an informed player, this agent pays a unitary cost to obtain this technology. A coalitional cost game can be defined from this situation, and the core of this game is known to be non- empty. We prove that the core of an information graph game is a von Neumann-Morgenstern stable set if and only if the graph is cycle- complete, or equivalently if the information graph game is concave. When the graph is not cycle-complete, whether there always exists a stable set is an open question. In this regard, we show that if the information graph consists of a ring that contains the source, then a stable set always exists and it is the core of a related information graph situation where one edge has been deleted.

If you wish to receive a link for the zoom meeting on the day of the event, please send an email to Tamás Solymosi (tamas dot solymosi at uni dash corvinus dot hu)

There are many ways of measuring the influence of scientific journals. We will survey most of these measures but in this talk we will focus on two important measures of journal impact (EF and SJR) both employing a similar algorithm to the PageRank algorithm. We will explain in detail how these indicators are computed and provide axiomatic characterizations to underline their employments. Finally, we will discuss where and how these indicators are applied, and speak in general about journal and university rankings.

If you wish to receive a link for the zoom meeting on the day of the event, please send an email to Tamás Solymosi (tamas dot solymosi at uni dash corvinus dot hu)

We study how to rank candidates based on individual rankings via positional scoring rules. Each position in each individual ranking is worth a certain number of points; the total sum of pointsdetermines the aggregate ranking. Our selection principle is consistency: once one of the candidates is removed, we want the aggregate ranking to remain intact. This principle is crucial whenever the set of the candidates might change and the remaining rankingguides our actions: whom should we interview if our first choice got a better offer? Who gets the cup once the previous winner is convicted of doping? Which movie should a group watch if everyone already saw the recommender system’s first choice? Will addinga spoiler candidate rig the election?Unfortunately, no scoring rule is completely consistent, but there are weaker notions of consistency we can use. There are scoring rules which are consistent if we add or remove a unanimouswinner — such as an athlete with suspiciously strong results. Likewise, consistent for removing or adding a unanimous loser — such as a spoiler candidate in an election. While extremely permissive individually, together these two criteria pin down a one-parameterfamily with the geometric sequence of scores. These geometric scoring rules include Borda count, generalised plurality (medal count), and generalised antiplurality (threshold rule) as edge cases, and we provide elegant new axiomatisations of these rules. Finally,we demonstrate how the one-parameter formulation can simplify the selection of suitable scoring rules for particular scenarios.

If you wish to receive a link for the zoom meeting on the day of the event, please send an email to Tamás Solymosi (tamas dot solymosi at uni dash corvinus dot hu)

Details here: http://afml.uni-corvinus.hu/

The presentation is a broad-brush summary of the overarching theme of my research with cherry-picking the latest and/or best papers. Briefly, using examples from my papers I attempt to show that sustainable competitive advantage, to a great extent, can be explained with soft, infrastructural factors that present the hardest barriers to imitation. Additionally, and informally, relying on my academic experience in Hungary, in the United States and in Europe, I offer three lessons for consideration for those who are willing to consider them.

If you wish to receive a link for the zoom meeting on the day of the event, please send an email to Tamás Solymosi (tamas dot solymosi at uni dash corvinus dot hu)

In this presentation, we present an overview of the characterization of properties of several classes of coloring games in terms of the underlying graph.

First, we discuss the class of minimum coloring games introduced by Deng et al. (1999). Here totally balancedness, existence of PMAS and submodularity are characterized by perfect graphs, 2K2P4 -free graphs and complete r-partite graphs, respectively (cf. Deng et al. (2000), Hamers et al. (2014), Okamoto (2003)).

Second, we discuss the class of weighted minimum coloring games introduced by Hamers et al. (2019). Here global (local) totally balancedness and global (local) submodularity are characterized by perfect graphs (any graph) and complete r-partite graphs (2K2P4 -free graphs), respectively.

Finally, we discuss the class of multiple player coloring games introduced in Hamers et al. (2020). Here we present some preliminary results.

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Deng, X., Ibaraki, T., Nagamochi, H., 1999. Algorithmic aspects of the core of combinatorial optimization games. Mathematics of Operations Research 24(3), 751–766.

Deng, X., Ibaraki, T., Nagamochi, H., Zang, W., 2000. Totally balanced combinatorial optimization games. Mathematical Programming 87, 441–452.

Hamers, H., Miquel, S., Norde, H., 2014. Monotonic stable solutions for minimum coloring games. Mathematical Programming 145, 509–529.

Hamers, H., Horozoglu, N., Norde, H., Tornoe Platz, T. On totally balanced, submodular and PMAS-admissible weighted minimum coloring games (submitted).

Hamers, H., Miquel, S., Norde, H., Obadi, S. On submodular multiple minimum coloring games (in preparation).

Okamoto, Y., 2003. Submodularity of some classes of the combinatorial optimization games. Mathematical Methods of Operations Research 58(1), 131–139.

If you wish to receive a link for the zoom meeting on the day of the event, please send an email to Tamás Solymosi (tamas dot solymosi at uni dash corvinus dot hu)