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## Publications

Publications (86)

In this paper, we propose the application of matching mechanisms to handle horizontal collaboration in logistics. Based on the requirements of a real-life setting, we introduce a new variation of matching under preferences. We provide a Random Serial Dictatorship (RSD) mechanism for finding a solution that incorporates Pareto optimality, incentive...

The max-cut problem is a fundamental combinatorial optimisation problem, with many applications. Poljak and Turzik found some facet-defining inequalities for the associated polytope, which we call 2-circulant inequalities. We present a more general family of facet-defining inequalities, an exact separation algorithm that runs in polynomial time, an...

We study a relocation problem which consists of allocating a given number of refugees—who are heterogeneous with respect to country of origin and characteristics such as gender, age or educational level—from Greece to other European Union countries which have pledged to accept a certain number of refugees. In order to study this problem, we develop...

We examine a novel variant of multitype capacitated facility location, motivated by two contemporary applications in parcel delivery and in managed printing services. Our setting is characterized by nonlinear functions for the setup cost of multiple facilities in a location and the service cost of multiple clients by a facility, capacities on both...

Energy and carbon management systems (ECMS) are a class of green information systems that has the potential to increase environmental sustainability in organizations and across supply chains. Employing a design science research approach, we define the scope of ECMS in the supply chain context, identify requirements, design an expository instantiati...

Refineries execute a series of interlinked processes, where the product of one unit serves as the input to another process. Potential failures within these processes affect the quality of the end products, operational efficiency, and revenue of the entire refinery. In this context, implementation of a real-time cognitive module, referring to predic...

Refineries execute a series of interlinked processes, where the product of one unit serves as the input to another process. Potential failures within these processes affect the quality of the end products, operational efficiency, and revenue of the entire refinery. In this context, implementation of a real-time cognitive module, referring to predic...

This work considers the production scheduling of the weaving process in a real-life textile industry, where a set of jobs - linked to the production of a fabric type and accompanied by a quantity - arrive over time and have to be processed (woven) by a set of parallel unrelated machines (looms) with respect to their strict deadlines (delivery dates...

Abstract
Energy and Carbon Management Systems (ECMS) are a class of green information systems that has the potential to increase environmental sustainability in organizations and across supply chains. Employing a design science research approach, we define the scope of ECMS in the supply chain context, identify requirements, design an expository i...

Energy and Carbon Management Systems (ECMS) are a class of green information systems that has the potential to increase environmental sustainability in organizations and across supply chains. Employing a design science research approach, we define the scope of ECMS in the supply chain context, identify requirements, design an expository instantiati...

We introduce and study weighted bipartite matching problems under strict preferences where blocking edges can be paid for, thus imposing costs rather than constraints as in classical models. We focus on the setting in which the weight of an edge represents the benefit from including it in the matching and/or the cost if it is a blocking edge. We sh...

This paper studies a real-life inter-modal freight transportation problem, comprised by three consecutive stages: disposition where orders are picked up by trucks, transferred and unloaded to a set of warehouses in Central and Eastern Europe, inter-region transport where the orders are packed into trailers, which are shipped to warehouses in Turkey...

We investigate a market without money in which agents can offer certain goods (or multiple copies of an agent-specific good) in exchange for goods of other agents. The exchange must be balanced in the sense that each agent should receive a quantity of good(s) equal to the one she transfers to others. In addition, each agent has strict preferences o...

Manufacturing systems are often prone to disruptions that break the continuity of operations and prevent them from reaching their planned performance. This paper presents a Situation-Aware Manufacturing System framework that is applied to identify and predict disruptions, to evaluate their impact and to react timely to repair the affected processes...

The emergence of the industrial internet of things that drives the fourth industrial revolution, also known as Industry 4.0 (I4.0), is bringing to the forefront the question of how industrial actors can capture value using such technologies. To answer this question, this paper follows a multidisciplinary approach drawing from the fields of Business...

The matroid parity (MP) problem is a powerful (and NP-hard) extension of the matching problem. Whereas matching polytopes are well understood, little is known about MP polytopes. We prove that, when the matroid is laminar, the MP polytope is affinely congruent to a perfect b-matching polytope. From this we deduce that, even when the matroid is not...

An upper bound on the diameter of the Stable Matching (Stable Marriage) polytope is known to be ⌊n2⌋ where n is the number of men (or women) involved in the matching. The current work complements that result by providing a lower bound and an algorithm computing it. It also presents a class of Stable Matching instances for which the lower bound coin...

The realization of stable b-matchings as matroid kernels yields the existing linear description of the stable b-matching (MM) problem. We revisit that description to derive the dimension, the facets, and the minimum equation system of the stable b-matching polytope. The derived minimal description includes O(m) constraints, m being the number of pa...

This paper describes an innovative approach to adopt the next-generation manufacturing paradigm based on flexible production units and eco-systems that can be quickly reprogrammed to provide fast time-to-market responses to global consumer demand, address mass-customisation needs and bring life to innovative products. The approach utilises the capa...

Submodularity defines a general framework rich of important theoretical properties while accommodating numerous applications. Although the notion has been present in the literature of Combinatorial Optimization for several decades, it has been overlooked in the analysis of global constraints. The current work illustrates the potential of submodular...

We consider Pareto optimal matchings (POMs) in a many-to-many market of applicants and courses where applicants have preferences, which may include ties, over individual courses and lexicographic preferences over sets of courses. Since this is the most general setting examined so far in the literature, our work unifies and generalizes several known...

Manufacturing companies are forced to become energy-aware under the pressure of energy costs, legislation and consumers’ environmental awareness. Production scheduling remains a critical decision making process, although demanding in computational terms and sensitive on data availability and credibility. Hence the interest in incorporating energy-r...

We consider the user selection downlink MU-MIMO scheduling problem in the practical case where there are more users than transmit antennas. First, we deduce a number of structural properties for the sum data rate maximization function under the reduced-complexity suboptimal approaches of zero-forcing dirty-paper (ZF-DP) and zero-forcing beamforming...

We address the problem of completability for 2-row orthogonal Latin rectangles (OLR2). The approach is to identify all incomplete pairs of 2-row Latin rectangles that are not completable to an OLR2 and are minimal with respect to this property; i.e., we characterize all circuits of the independence system associated with OLR2. Since there can be no...

A critical step in a cutting plane algorithm is separation, i.e., establishing whether a given vector x violates an inequality belonging to a specific class. It is customary to express the time complexity of a separation algorithm in the number of variables n. Here, we argue that a separation algorithm may instead process the vector containing the...

We address the problem of completability for 2-row orthogonal Latin rectangles (OLR2).
Our approach is to identify all pairs of incomplete 2-row Latin rectangles that are not com-
pletable to an OLR2 and are minimal with respect to this property; i.e., we characterize
all circuits of the independence system associated with OLR2. Since there can be...

We consider the user selection downlink MU-MIMO scheduling problem in the practical case where there are more users than transmit antennas. First, we deduce a number of structural properties for the sum data rate maximization function under the reduced-complexity suboptimal approaches of zero-forcing dirty-paper (ZF-DP) and zero-forcing beamforming...

We consider Pareto-optimal matchings (POMs) in a many-to-many market of applicants and courses where applicants have preferences, which may include ties, over individual courses and lexicographic preferences over sets of courses. Since this is the most general setting examined so far in the literature, our work unifies and generalizes several known...

We consider Pareto-optimal matchings (POMs) in a many-to-many market of
applicants and courses where applicants have preferences, which may include
ties, over individual courses and lexicographic preferences over sets of
courses. Since this is the most general setting examined so far in the
literature, our work unifies and generalizes several known...

In response to the mounting request for sustainable supply chains, companies need to assess the environmental performance of their operations and products. Recent studies within the field of Information Systems (IS) argue that information systems can forge supply chain sustainability by monitoring a firm's environmental performance. The latter requ...

Consider a many-to-many matching market that involves two finite disjoint sets, a set AA of applicants and a set CC of courses. Each applicant has preferences on the different sets of courses she can attend, while each course has a quota of applicants that it can admit. In this paper, we examine Pareto optimal matchings (briefly POM) in the context...

Cardinality constraints have received considerable attention from the Constraint Programming community as (so-called) global constraints that appear in the formulation of several real-life problems, while also having an interesting combinatorial structure. After discussing the relation of cardinality constraints with well-known combinatorial proble...

We describe a new coordination mechanism for non-atomic congestion games that
leads to a (selfish) social cost which is arbitrarily close to the non-selfish
optimal. This mechanism does not incur any additional extra cost, like tolls,
which are usually differentiated from the social cost as expressed in terms of
delays only.

Environmental concerns, stricter legislation and inflated energy costs, together yield energy efficiency as an important pillar for virtually every industrial sector. Mindful of this challenge, ISs can act as enablers of energy-based management and intelligent decision support. Based on empirical evidence through two case studies combined with the...

The diameter of the stable matching (stable marriage) polytope is bounded from above by [n/2], where n is the number of men (or women) involved in the matching; this bound is attainable.

In the setting of the stable matching (SM) problem, it has been observed that some of the man-woman pairs cannot be removed although they participate in no stable matching, since such a removal would alter the set of solutions. These pairs are yet to be identified. Likewise (and despite the sizeable literature), some of the fundamental characterist...

The global cardinality constraint (gcc) [7], written as
$$ cardinality(x,J;l,u),x_{j}\in D_{j},j\in J, $$ states that each value d is received by at least ld and by at most ud of the variables {xj:j ∈ J}, where \(d\in D={\mathop{\textstyle \bigcup }}_{j\in J}D_{j}=\{0,\ldots ,|D|-1\};\) also, 0 ≤ ld ≤ ud and ud ≥ 1 for all d ∈ D. The gcc has severa...

An implicit linear description of the stable matching polytope is provided in terms of the blocker and antiblocker sets of constraints of the matroid-kernel polytope. The explicit identification of both these sets is based on a partition of the stable pairs in which each agent participates. Here, we expose the relation of such a partition to rotati...

This paper investigates the production efficiency of 12 European banking systems over the period 1997-2004, taking into account possible technology heterogeneity. Using a non-parametric metafrontier framework, efficiency and metatechnology ratio measures are computed and decomposed into input- and output-invariant components. Empirical findings ind...

This paper investigates the production efficiency of 12 European banking systems over the period 1997–2004, taking into account possible technology heterogeneity. Using a non-parametric metafrontier framework, efficiency and metatechnology ratio measures are computed and decomposed into input- and output-invariant components. Empirical findings ind...

Energy Efficient Technologies (EET) have attracted strong interest because of their role in reducing environmental damage. Their adoption, however, remains rather low, while their impact on productivity is substantial and differentiating with respect to technological characteristics. Energy intensity, being such an obvious characteristic, could be...

The many-to-many stable matching problem (MM), defined in the context of a job market, asks for an assignment of workers to firms satisfying the quota of each agent and being stable, pairwise or setwise, with respect to given preference lists or relations. In this paper, we propose a time-optimal algorithm that identifies all stable worker--firm pa...

In polyhedral combinatorics, the polytope related to a combinatorial optimization problem is examined in order to obtain families of valid inequalities. To incorporate such families of inequalities within a ‘Branch & Cut' algorithm requires one further step: that of deriving an algorithm which determines whether an inequality of a specific family i...

Wheel structures of the Orthogonal Latin Squares (OLS) polytope (PI) are presented in (2). The current work focuses on the families of valid inequalities arising from wheels and proves that certain among them are facet-defining for PI. For two of these families we provide ecient separation procedures. We also present results regarding odd-hole ineq...

This paper examines the facial structure of the convex hull of integer vectors satisfying a system of alldifferent predicates, also called an alldifferent system. The underlying analysis is based on a property, called inclusion, pertinent to such a system. For the alldifferent systems for which this property holds, we present two families of facet-...

The many-to-many Stable Matching (MM) problem is defined on a set of workers and a set of firms and asks for an allocation of workers to firms that satisfies the firms' quotas and the preferences of workers for firms and vice-versa. This article proposes a time-optimal algorithm for solving the minimum-regret problem for the MM, i.e. the problem of...

A fundamental step in any cutting plane algorithm is separation: deciding whether a violated inequality exists within a certain class of inequalities. It is customary to express the complexity of a separation algorithm in n, the number of variables. Here, we argue that the input to a separation algorithm can be expressed in jsup(x)j, where sup(x) d...

We study the facial structure of the alldifferent system, i.e., the polytope (namely, PI ) defined as the convex hull of integer vectors satisfying such a system. We derive classes of facets for PI by examining induced subgraphs of the associated constraint graph. Some of these graphic structures (for example, odd holes, webs, etc.) are well known...

A Latin square is an n × n matrix where in each row and each column every number between 1 and n appears exactly once. A Latin square can be described by a binary vector with n components, and the Latin square polytope (Pn;I) is the convex hull of such binary vectors. We study the facial structure of Pn;I by examining valid inequalities induced by...

The (k,s)assignment problem sets a unified framework for studying the facial structure of families of assignment polytopes. Through this framework, we derive classes of clique facets for all axial and planar assignment polytopes. For each of these classes, a polynomial-time separation procedure is described. Furthermore, we provide computational ex...

This paper examines firms operating under different technologies but under a common metatechnology and provides a decomposition of their efficiency into input-invariant and output-invariant components. To achieve this, it reviews known definitions of technical and scale efficiency and provides alternative expressions, which incorporate a firm opera...

In this paper, we show that for any independence system, the problem of finding a persistency partition of the ground set
and that of finding a maximum weight independent set are polynomially equivalent.

The safety in the transport sector is an indicator for sustainability. Given its importance for the overall economic development and the malfunctions caused due to a possible drawback in the transport sector development different systems cater for the advancement of safety during transport. Safety is quite critical with reference to perishable good...

This paper presents an artificial, i.e. computer-based, market that models various auctions for emissions permits. A brief This paper presents an artificial, i.e. computer-based, market that models various auctions for emissions permits. A brief
analysis of the existing auctions for emission permits provides the motivation for introducing a new typ...

Orthogonal Latin squares (OLS) are fundamental combinatorial objects with important theoretical properties and interesting applications. OLS can be represented by integer points satisfying a certain system of equalities. The convex hull of these points is the OLS polytope. This paper adds to the description of the OLS polytope by providing non-triv...

This paper presents an algorithm achieving hyperarc consistency for the stable admissions problem and discusses computational results.

Recent advances in information technology have raised the issue of the extent to which the potential benefits gained by Radio Frequency Identification (RFID) outweigh the value of investment in such an initiative. Hence, this has become a matter of considerable concern and debate for both practitioners and academics alike. In view of the pre-mature...

The addition of mobile wireless identification technologies to provide persistent identifiers for food products will become a key mechanism to enhance the consumer experience. This paper presents the use of RFID track and tracing technology to help create a safer and more manageable mobile mean of transporting perishable comestibles with trucks ove...

This paper applies algorithms integrating Integer Programming (IP) and Constraint Programming (CP) to the Mutually Orthogonal Latin Squares (MOLS) problem. We investigate the behaviour of these algorithms against traditional IP and CP schemes. Computational results are obtained with respect to various aspects of the algorithms, using instances of t...

Finding a maximum cardinality matching in a graph is a problem appearing in numerous settings. The problem asks for a set of edges of maximum cardinality, such that no two edges of this set have an endpoint in common. The variety of applications of this problem, along with the fact that several logic predicates can be modelled after it, motivates t...

We investigate an integer programming model for multi-dimensional assignment problems. This model enables us to establish the dimension for entire families of assignment polytopes, thus unifying and generalising previous results. In particular, we establish the dimension of the linear assignment polytope as well as that of every axial and planar as...

Let G(V,E) denote an undirected graph, V and E being the sets of its nodes and edges, respectively. A matching in G(V,E) is a subset of edges with no common endpoints. Finding a matching of maximum cardinality constitutes the maximum cardinality
matching (MCM) problem. For a thorough theoretical discussion we refer to [6]. The MCM problem is of spe...

Latin squares of order n have a 1–1 correspondence with the feasible solutions of the 3-index planar assignment problem (3PAPn). In this paper, we present a new class of facets for the associated polytope, induced by odd-hole inequalities.

Since 1782, when Euler addressed the question of existence of a pair of orthogonal Latin squares (OLS) by stating his famous conjecture, these structures have remained an active area of research. In this paper, we examine the polyhedral aspects of OLS. In particular, we establish the dimension of the OLS polytope, describe all cliques of the underl...

In this chapter we present various equivalent formulations or models for the Mutually Orthogonal Latin Squares (MOLS) problem
and its generalization. The most interesting feature of the problem is that for some parameters the problem may be infeasible.
Our evaluation of different formulations is geared to tackling this feasibility problem. Starting...

A wheel in a graph G(V,E) is an induced subgraph consisting of an odd hole and an additional node connected to all nodes of the hole. In this paper,
we study the wheels of the intersection graph of the Orthogonal Latin Squares polytope (PI). Our work builds on structural properties of wheels which are used to categorise them into a number of collec...

The polytope defined by the convex hull of integer vectors satisfying the system of the two all_different predicates was examined. The dimension of this polytope was established and subsequently two classes of facet-defining inequalities were also exhibited. A separation algorithm of low complexity, which provided only the facet-defining inequaliti...

This paper presents an alternative proof for the non-existence of orthogonal Latin squares of order 6. Our method is algebraic, rather than enumerative, and applies linear programming in order to obtain appropriate dual vectors. The proof is achievable only after extending previously known results for symmetry elimination.

This paper examines sets of all_different predicates that appear in multidimensional assignment problems. It proposes the
study of certain LP relaxations as a prerequisite of integrating CP with IP on these problems. The convex hull of vectors
satisfying simultaneously two predicates is analysed and a separation algorithm for facet-defining inequal...

In this paper, we examine the orthogonal Latin squares (OLS) problem from an integer programming perspective. The OLS problem has a long history and its significance arises from both theoretical aspects and practical applications. The problem is formulated as a four-index assignment problem whose solutions correspond to OLS. This relationship is ex...

Load balancing/sharing is a policy which exploits the communication facility between the servers of a distributed system, by using the exchanging of status information and jobs between any two servers of the system, in order to improve the performance of the whole system. In this work, we propose a new adaptive distributed hierarchical scheme, the...

A wheel in a graph G(V, E) is an induced subgraph consisting of an odd hole and an additional node connected to all nodes of the hole. In this paper, we study the wheels of the column intersection graph of the OLS polytope (P I). These structures induce valid inequalities for this polytope, which are facet defining for its set packing relaxation. O...

This thesis examines the Orthogonal Latin Squares (OLS) problem from the viewpoint of Integer and Constraint programming. An Integer Programming (IP) model is proposed and the associated polytope is analysed. We identify several families of strong valid inequalities, namely inequalities arising from cliques, odd holes, antiwebs and wheels of the as...

We consider the problem of Mutually Orthogonal Latin Squares and propose two algorithms which integrate Integer Programming
(IP) and Constraint Programming (CP). Their behaviour is examined and compared to traditional CP and IP algorithms. The results
assess the quality of inference achieved by the CP and IP, mainly in terms of early identification...

This paper introduces an Integer Programming model for multidimensional assignment problems and examines the underlying polytopes. It also proposes a certain hierarchy among assignment polytopes. The dimension for classes of multidimensional assignment polytopes is established, unifying and generalising previous results. The framework introduced co...

Since 1782, when Euler addressed the question of existence of a pair of Orthogonal Latin Squares (OLS) by stating his famous conjecture ([8, 9, 13]), these structures have remained an active area of research due to their theoretical properties as well as their applications in a variety of fields. In the current work we consider the polyhedral aspec...