A matematikai értelemben vett gráfok vagy hálózatok sokoldalú, szemléletes modellezési eszközt bi... more A matematikai értelemben vett gráfok vagy hálózatok sokoldalú, szemléletes modellezési eszközt biztosítanak más tudományterületek számára, többek között az orvostudomány számára is. Ebben a közleményben a fertőző betegségekkel kapcsolatos hálózati modelleket ismertetjük röviden. Az ismert, a tudományterület szakirodalmában meglévő eszközökön felül a fertőzési folyamatot kiválóan lehet modellezni hálózatokkal is. A téma életszerűségét kiválóan bizonyítja a használt modellek sokszínűsége, az alkalmazások sokoldalúsága és a témával kapcsolatos tudományos közlemények nagy száma. A téma méretéből adódóan ebben a közleményben csak a hálózatalapú járványterjedési modellek alapfogalmait és alapvető típusait tudjuk ismertetni, valamint néhány gyakorlati példával szemléltetjük alkalmazhatóságukat.
A central problem of public transportation companies is to optimize their operational process. Si... more A central problem of public transportation companies is to optimize their operational process. Since the minimization of the overall operational cost is a very complex task, the arising subproblems are considered as separeted optimization problems. Vehicle scheduling assigns the trips of the input to vehicles that execute them, while driver scheduling creates the daily duties of the drivers based on the vehicle schedules. In this presentation, we introduce a heuristic for the driver scheduling problem. Both vehicleand driver scheduling are NP hard [2, 3]. An exact solution for our problem can be found in [1], where the problem is presented as a set-covering problem, and is solved by column generation. Using this approach, optimal solution for a real-life instance of a middle-sized city (approximately 5000 trips) can take up to several weeks, as the number of possible driver duty combinations generated by the pricing problem is too large. This way, the method cannot be applied in practice, so we developed a heuristic to speed up the generation process. The method partitions the trips of the input into two sets based on their starting time. Trips starting "too late" are selected, and the driver scheduling problem is solved using these as an input. Suitable driver schedules of the solution are saved, while trips of the other schedules are joined with the remaining partition. Trips of this resulting partition are divided using time windows, and the problem is solved for each individual time window separately in a sequential manner. Each resulting schedule of a phase is considered as a single trip in the future, and joined with trips belonging to the next time window. With the decrease of the number of trips, this approach decreases the size of our problem significantly, and allows the exact method to solve the smaller sub-problems in an acceptable running time. Our new heuristic approach has been tested on real-life input. The test results show that running time significantly decreases, while the cost of the solutions remains close to the optimum.
Recycling waste materials has become increasingly important recently both for economic and enviro... more Recycling waste materials has become increasingly important recently both for economic and environmental reasons. In order to efficiently operate the backward flow of the materials, a basic challenge is to design the proper reverse logistics network containing the collection points, test centers and manufacturing plants. This paper studies the supply network of waste wood, which has to be collected in dedicated accumulation centers, and transported to processing facilities. We focus on the facility location of processing centers and propose mathematical models that take economies of scale and robustness into account, including a novel approach based on bilevel optimization. We also give a local and tabu search method for the solution of the problem. Test results are presented for both the robust and non-robust case using instances based on a real-life dataset.
A new methodology in temporal networks is presented for the use of fraud detection systems in the... more A new methodology in temporal networks is presented for the use of fraud detection systems in the banking sector. Standard approaches of fraudulence monitoring mainly have the focus on the individual client data. Our approach will concentrate on the hidden data produced by the network of the transaction database. The methodology is based on a cycle detection method with the help of which important patterns can be identified as shown by the test on real data. Our solution is integrated into a financial fraud system of a bank; the experimental results are demonstrated by a real-world case study.
A confluent and terminating reduction system is introduced for graphs, which preserves the number... more A confluent and terminating reduction system is introduced for graphs, which preserves the number of their perfect matchings. A union-find algorithm is presented to carry out reduction in almost linear time. The König property is investigated in the context of reduction by introducing the König deficiency of a graph G as the difference between the vertex covering number and the matching number of G. It is shown that the problem of finding the König deficiency of a graph is NP-complete even if we know that the graph reduces to the empty graph. Finally, the König deficiency of graphs G having a vertex v such that $$G-v$$G-v has a unique perfect matching is studied in connection with reduction.
Soliton automata are a graph theoretic model for electronic switching at the molecular level. In ... more Soliton automata are a graph theoretic model for electronic switching at the molecular level. In the design of soliton circuits, the deterministic property of the corresponding automata is of primary importance. The underlying graphs of such automata, called deterministic soliton graphs, are characterized in terms of graphs not having even-length cycles and graphs having a unique perfect matching. On the basis of this characterization, a modification of the currently most efficient unique perfect matching algorithm is worked out to decide in O(m log 4 n) time if a graph with n vertices and m edges defines a deterministic soliton automaton. A yet more efficient O(m) algorithm is given for the special case of chestnut and elementary soliton graphs. All of these algorithms are capable of constructing a state for the corresponding soliton automaton, and the general algorithm can also be used to simplify the automaton to an isomorphic elementary one.
Central European Journal of Operations Research, 2017
The pre-planned schedules of a transportation company are often disrupted by unforeseen events. A... more The pre-planned schedules of a transportation company are often disrupted by unforeseen events. As a result of a disruption, a new schedule has to be produced as soon as possible. This process is called the vehicle rescheduling problem, which aims to solve a single disruption and restore the order of transportation. However, there are multiple disruptions happening over a "planning unit" (usually a day), and all of them have to be addressed to achieve a final feasible schedule. From an operations management point of view the quality of the final solution has to be measured by the combined quality of every change over the horizon of the "planning unit", not by evaluating the solution of each disruption as a separate problem. The problem of finding an optimal solution where all disruptions of a "planning unit" are addressed will be introduced as the dynamic vehicle rescheduling problem (DVRSP). The disruptions of the DVRSP arrive in an online manner, but giving an optimal final schedule for the "planning unit" would mean knowing all information in advance. This is not possible in a real-life scenario, which means that heuristic solution methods have to be considered. In this paper, we present a recursive and a local search algorithm to solve the DVRSP. In order to measure the quality of the solutions given by the heuristics, we introduce the so-called quasi-static DVRSP, a theoretical problem where all the disruptions are known in advance. We give two mathematical models for this quasi-static problem, and use their optimal solutions to evaluate the quality of our heuristic results. The heuristic methods for the dynamic problem are tested on different random instances.
Soliton graphs are studied in the context of a reduction procedure that simplifies the structure ... more Soliton graphs are studied in the context of a reduction procedure that simplifies the structure of graphs without affecting the deterministic property of the corresponding automata. It is shown that an elementary soliton graph defines a deterministic automaton iff it reduces to a graph not containing even-length cycles. Based on this result, a general characterization is given for deterministic soliton graphs using chestnut graphs, generalized trees, and graphs having a unique perfect matching. Povzetek:Članek obravnava grafe brez lihih ciklov.
We study the switching aspects of molecular computing from a novel algebraic point of view. Our a... more We study the switching aspects of molecular computing from a novel algebraic point of view. Our approach is based on the concept indexed monoidal algebra, which provides an equivalent formalism for compact closed categories being used recently in the literature in connection with quantum computing. The point is to separate syntax, as the algebra G of graphs, from semantics, which is related to the algebra T of Turing automata, and define meaning as a homomorphism. Eventually, the syntax is restricted to the Gallai-Edmonds algebra G-E of graphs having a perfect internal matching, and the corresponding semantical structure, defined as the algebra S of soliton automata, is the quotient of an appropriate subalgebra of T .
Proceedings of the 9th International Conference on Applied Informatics, Volume 1, 2015
The application of data compression has an increasing importance in the data transfer on digital ... more The application of data compression has an increasing importance in the data transfer on digital networks. In the case of real time applications the limitations of these techniques are the compression/decompression time and the bandwidth of the network. In multicore environment the compression/decompression time is reducible with parallelism. OpenMP (Open Multi-Processing) is a compiler extension that enables to add parallelism into existing source code [1, 2]. It is available in most FORTRAN and C/C++ compilers. H.264 [3] is currently one of the most commonly used video compression format. Freeware version of H.264 is available in FFmpeg library [4]. This paper describes the use of OpenMP and H.264 library in multicore environment.
In the area of optimization of public transportation there are several methods for modeling and s... more In the area of optimization of public transportation there are several methods for modeling and solving vehicle and driver scheduling problems. We designed a sequential heuristic method for solving the combined (vehicle and driver scheduling) problem. Our model is based on a modification of the vehicle schedules to satisfy driver requirements. We introduced a driver friendly approach of the optimization of the scheduling, which is closer to the practice used by public transportation companies. We give test results for this, which are shown as illustrative example for the method in the scheduling of the bus trips of Szeged city, Hungary.
Central European Journal of Operations Research, 2012
The driver scheduling problem in public transportation is defined in the following way. There is ... more The driver scheduling problem in public transportation is defined in the following way. There is a set of operational tasks, and the goal is to define the sequence of these tasks as shifts in such a way that every task must be assigned to a shift without overlapping. In real-world situations several additional constraints need to be considered, which makes large practical problems challenging to be solved efficiently. In practice it is also an important request with respect to a public transportation scheduling system to offer several versions of quasi-optimal solutions. In this paper we present an efficient driver scheduling solution methodology which is flexible in the above sense.
Indoor Air Quality monitoring is a major asset to improving quality of life and building manageme... more Indoor Air Quality monitoring is a major asset to improving quality of life and building management. Today, the evolution of embedded technologies allows the implementation of such monitoring on the edge of the network. However, several concerns need to be addressed related to data security and privacy, routing and sink placement optimization, protection from external monitoring, and distributed data mining. In this paper, we describe an integrated framework that features distributed storage, blockchain-based Role-based Access Control, onion routing, routing and sink placement optimization, and distributed data mining to answer these concerns. We describe the organization of our contribution and show its relevance with simulations and experiments over a set of use cases.
Advances in public transit modeling and smart card technologies can reveal detailed contact patte... more Advances in public transit modeling and smart card technologies can reveal detailed contact patterns of passengers. A natural way to represent such contact patterns is in the form of networks. In this paper we utilize known contact patterns from a public transit assignment model in a major metropolitan city, and propose the development of two novel network structures, each of which elucidate certain aspects of passenger travel behavior. We first propose the development of a transfer network, which can reveal passenger groups that travel together on a given day. Second, we propose the development of a community network, which is derived from the transfer network, and captures the similarity of travel patterns among passengers. We then explore the application of each of these network structures to identify the most frequently used travel paths, i.e., routes and transfers, in the public transit system, and model epidemic spreading risk among passengers of a public transit network, resp...
2018 4th International Conference on Logistics Operations Management (GOL), 2018
Papers dealing with optimization problems in public transportation usually follow the same method... more Papers dealing with optimization problems in public transportation usually follow the same methodology. The problem is modeled in a classical mathematical way, and then either solved directly using mathematical programming methods, or by the application of combinatorial heuristics. Even if this process yields an optimal solution, it might prove complicated to apply the achieved results directly in practice. In a transportation system, solutions for individual problems are only part of a more complex process, and they are often used only to aid experts in making decisions. However, the structure of the problem and the steps taken to achieve the solution are often lost in the solution process, while they might prove extremely useful to a human planner. This paper introduces a linearly priced timed automata model for the bus schedule assignment problem. With its help, the steps taken to achieve any feasible solution of the problem can be easily reconstructed, providing another tool for human experts to use in their decision planning process.
A complexity analysis based on the structure of perfect matchings is given for the most efficient... more A complexity analysis based on the structure of perfect matchings is given for the most efficient basic filtering algorithms in constraint programming with respect to the role of edges in matchings.
In this paper we introduce an information system for optimizing public transportation. We integra... more In this paper we introduce an information system for optimizing public transportation. We integrated state-of-the-art results o f the literature and new methods developed by our team. The main results of the research presented in this paper are not just the successful applications of these methods, but a new approach for system design in decision support of public transportation optimization processes.
A matematikai értelemben vett gráfok vagy hálózatok sokoldalú, szemléletes modellezési eszközt bi... more A matematikai értelemben vett gráfok vagy hálózatok sokoldalú, szemléletes modellezési eszközt biztosítanak más tudományterületek számára, többek között az orvostudomány számára is. Ebben a közleményben a fertőző betegségekkel kapcsolatos hálózati modelleket ismertetjük röviden. Az ismert, a tudományterület szakirodalmában meglévő eszközökön felül a fertőzési folyamatot kiválóan lehet modellezni hálózatokkal is. A téma életszerűségét kiválóan bizonyítja a használt modellek sokszínűsége, az alkalmazások sokoldalúsága és a témával kapcsolatos tudományos közlemények nagy száma. A téma méretéből adódóan ebben a közleményben csak a hálózatalapú járványterjedési modellek alapfogalmait és alapvető típusait tudjuk ismertetni, valamint néhány gyakorlati példával szemléltetjük alkalmazhatóságukat.
A central problem of public transportation companies is to optimize their operational process. Si... more A central problem of public transportation companies is to optimize their operational process. Since the minimization of the overall operational cost is a very complex task, the arising subproblems are considered as separeted optimization problems. Vehicle scheduling assigns the trips of the input to vehicles that execute them, while driver scheduling creates the daily duties of the drivers based on the vehicle schedules. In this presentation, we introduce a heuristic for the driver scheduling problem. Both vehicleand driver scheduling are NP hard [2, 3]. An exact solution for our problem can be found in [1], where the problem is presented as a set-covering problem, and is solved by column generation. Using this approach, optimal solution for a real-life instance of a middle-sized city (approximately 5000 trips) can take up to several weeks, as the number of possible driver duty combinations generated by the pricing problem is too large. This way, the method cannot be applied in practice, so we developed a heuristic to speed up the generation process. The method partitions the trips of the input into two sets based on their starting time. Trips starting "too late" are selected, and the driver scheduling problem is solved using these as an input. Suitable driver schedules of the solution are saved, while trips of the other schedules are joined with the remaining partition. Trips of this resulting partition are divided using time windows, and the problem is solved for each individual time window separately in a sequential manner. Each resulting schedule of a phase is considered as a single trip in the future, and joined with trips belonging to the next time window. With the decrease of the number of trips, this approach decreases the size of our problem significantly, and allows the exact method to solve the smaller sub-problems in an acceptable running time. Our new heuristic approach has been tested on real-life input. The test results show that running time significantly decreases, while the cost of the solutions remains close to the optimum.
Recycling waste materials has become increasingly important recently both for economic and enviro... more Recycling waste materials has become increasingly important recently both for economic and environmental reasons. In order to efficiently operate the backward flow of the materials, a basic challenge is to design the proper reverse logistics network containing the collection points, test centers and manufacturing plants. This paper studies the supply network of waste wood, which has to be collected in dedicated accumulation centers, and transported to processing facilities. We focus on the facility location of processing centers and propose mathematical models that take economies of scale and robustness into account, including a novel approach based on bilevel optimization. We also give a local and tabu search method for the solution of the problem. Test results are presented for both the robust and non-robust case using instances based on a real-life dataset.
A new methodology in temporal networks is presented for the use of fraud detection systems in the... more A new methodology in temporal networks is presented for the use of fraud detection systems in the banking sector. Standard approaches of fraudulence monitoring mainly have the focus on the individual client data. Our approach will concentrate on the hidden data produced by the network of the transaction database. The methodology is based on a cycle detection method with the help of which important patterns can be identified as shown by the test on real data. Our solution is integrated into a financial fraud system of a bank; the experimental results are demonstrated by a real-world case study.
A confluent and terminating reduction system is introduced for graphs, which preserves the number... more A confluent and terminating reduction system is introduced for graphs, which preserves the number of their perfect matchings. A union-find algorithm is presented to carry out reduction in almost linear time. The König property is investigated in the context of reduction by introducing the König deficiency of a graph G as the difference between the vertex covering number and the matching number of G. It is shown that the problem of finding the König deficiency of a graph is NP-complete even if we know that the graph reduces to the empty graph. Finally, the König deficiency of graphs G having a vertex v such that $$G-v$$G-v has a unique perfect matching is studied in connection with reduction.
Soliton automata are a graph theoretic model for electronic switching at the molecular level. In ... more Soliton automata are a graph theoretic model for electronic switching at the molecular level. In the design of soliton circuits, the deterministic property of the corresponding automata is of primary importance. The underlying graphs of such automata, called deterministic soliton graphs, are characterized in terms of graphs not having even-length cycles and graphs having a unique perfect matching. On the basis of this characterization, a modification of the currently most efficient unique perfect matching algorithm is worked out to decide in O(m log 4 n) time if a graph with n vertices and m edges defines a deterministic soliton automaton. A yet more efficient O(m) algorithm is given for the special case of chestnut and elementary soliton graphs. All of these algorithms are capable of constructing a state for the corresponding soliton automaton, and the general algorithm can also be used to simplify the automaton to an isomorphic elementary one.
Central European Journal of Operations Research, 2017
The pre-planned schedules of a transportation company are often disrupted by unforeseen events. A... more The pre-planned schedules of a transportation company are often disrupted by unforeseen events. As a result of a disruption, a new schedule has to be produced as soon as possible. This process is called the vehicle rescheduling problem, which aims to solve a single disruption and restore the order of transportation. However, there are multiple disruptions happening over a "planning unit" (usually a day), and all of them have to be addressed to achieve a final feasible schedule. From an operations management point of view the quality of the final solution has to be measured by the combined quality of every change over the horizon of the "planning unit", not by evaluating the solution of each disruption as a separate problem. The problem of finding an optimal solution where all disruptions of a "planning unit" are addressed will be introduced as the dynamic vehicle rescheduling problem (DVRSP). The disruptions of the DVRSP arrive in an online manner, but giving an optimal final schedule for the "planning unit" would mean knowing all information in advance. This is not possible in a real-life scenario, which means that heuristic solution methods have to be considered. In this paper, we present a recursive and a local search algorithm to solve the DVRSP. In order to measure the quality of the solutions given by the heuristics, we introduce the so-called quasi-static DVRSP, a theoretical problem where all the disruptions are known in advance. We give two mathematical models for this quasi-static problem, and use their optimal solutions to evaluate the quality of our heuristic results. The heuristic methods for the dynamic problem are tested on different random instances.
Soliton graphs are studied in the context of a reduction procedure that simplifies the structure ... more Soliton graphs are studied in the context of a reduction procedure that simplifies the structure of graphs without affecting the deterministic property of the corresponding automata. It is shown that an elementary soliton graph defines a deterministic automaton iff it reduces to a graph not containing even-length cycles. Based on this result, a general characterization is given for deterministic soliton graphs using chestnut graphs, generalized trees, and graphs having a unique perfect matching. Povzetek:Članek obravnava grafe brez lihih ciklov.
We study the switching aspects of molecular computing from a novel algebraic point of view. Our a... more We study the switching aspects of molecular computing from a novel algebraic point of view. Our approach is based on the concept indexed monoidal algebra, which provides an equivalent formalism for compact closed categories being used recently in the literature in connection with quantum computing. The point is to separate syntax, as the algebra G of graphs, from semantics, which is related to the algebra T of Turing automata, and define meaning as a homomorphism. Eventually, the syntax is restricted to the Gallai-Edmonds algebra G-E of graphs having a perfect internal matching, and the corresponding semantical structure, defined as the algebra S of soliton automata, is the quotient of an appropriate subalgebra of T .
Proceedings of the 9th International Conference on Applied Informatics, Volume 1, 2015
The application of data compression has an increasing importance in the data transfer on digital ... more The application of data compression has an increasing importance in the data transfer on digital networks. In the case of real time applications the limitations of these techniques are the compression/decompression time and the bandwidth of the network. In multicore environment the compression/decompression time is reducible with parallelism. OpenMP (Open Multi-Processing) is a compiler extension that enables to add parallelism into existing source code [1, 2]. It is available in most FORTRAN and C/C++ compilers. H.264 [3] is currently one of the most commonly used video compression format. Freeware version of H.264 is available in FFmpeg library [4]. This paper describes the use of OpenMP and H.264 library in multicore environment.
In the area of optimization of public transportation there are several methods for modeling and s... more In the area of optimization of public transportation there are several methods for modeling and solving vehicle and driver scheduling problems. We designed a sequential heuristic method for solving the combined (vehicle and driver scheduling) problem. Our model is based on a modification of the vehicle schedules to satisfy driver requirements. We introduced a driver friendly approach of the optimization of the scheduling, which is closer to the practice used by public transportation companies. We give test results for this, which are shown as illustrative example for the method in the scheduling of the bus trips of Szeged city, Hungary.
Central European Journal of Operations Research, 2012
The driver scheduling problem in public transportation is defined in the following way. There is ... more The driver scheduling problem in public transportation is defined in the following way. There is a set of operational tasks, and the goal is to define the sequence of these tasks as shifts in such a way that every task must be assigned to a shift without overlapping. In real-world situations several additional constraints need to be considered, which makes large practical problems challenging to be solved efficiently. In practice it is also an important request with respect to a public transportation scheduling system to offer several versions of quasi-optimal solutions. In this paper we present an efficient driver scheduling solution methodology which is flexible in the above sense.
Indoor Air Quality monitoring is a major asset to improving quality of life and building manageme... more Indoor Air Quality monitoring is a major asset to improving quality of life and building management. Today, the evolution of embedded technologies allows the implementation of such monitoring on the edge of the network. However, several concerns need to be addressed related to data security and privacy, routing and sink placement optimization, protection from external monitoring, and distributed data mining. In this paper, we describe an integrated framework that features distributed storage, blockchain-based Role-based Access Control, onion routing, routing and sink placement optimization, and distributed data mining to answer these concerns. We describe the organization of our contribution and show its relevance with simulations and experiments over a set of use cases.
Advances in public transit modeling and smart card technologies can reveal detailed contact patte... more Advances in public transit modeling and smart card technologies can reveal detailed contact patterns of passengers. A natural way to represent such contact patterns is in the form of networks. In this paper we utilize known contact patterns from a public transit assignment model in a major metropolitan city, and propose the development of two novel network structures, each of which elucidate certain aspects of passenger travel behavior. We first propose the development of a transfer network, which can reveal passenger groups that travel together on a given day. Second, we propose the development of a community network, which is derived from the transfer network, and captures the similarity of travel patterns among passengers. We then explore the application of each of these network structures to identify the most frequently used travel paths, i.e., routes and transfers, in the public transit system, and model epidemic spreading risk among passengers of a public transit network, resp...
2018 4th International Conference on Logistics Operations Management (GOL), 2018
Papers dealing with optimization problems in public transportation usually follow the same method... more Papers dealing with optimization problems in public transportation usually follow the same methodology. The problem is modeled in a classical mathematical way, and then either solved directly using mathematical programming methods, or by the application of combinatorial heuristics. Even if this process yields an optimal solution, it might prove complicated to apply the achieved results directly in practice. In a transportation system, solutions for individual problems are only part of a more complex process, and they are often used only to aid experts in making decisions. However, the structure of the problem and the steps taken to achieve the solution are often lost in the solution process, while they might prove extremely useful to a human planner. This paper introduces a linearly priced timed automata model for the bus schedule assignment problem. With its help, the steps taken to achieve any feasible solution of the problem can be easily reconstructed, providing another tool for human experts to use in their decision planning process.
A complexity analysis based on the structure of perfect matchings is given for the most efficient... more A complexity analysis based on the structure of perfect matchings is given for the most efficient basic filtering algorithms in constraint programming with respect to the role of edges in matchings.
In this paper we introduce an information system for optimizing public transportation. We integra... more In this paper we introduce an information system for optimizing public transportation. We integrated state-of-the-art results o f the literature and new methods developed by our team. The main results of the research presented in this paper are not just the successful applications of these methods, but a new approach for system design in decision support of public transportation optimization processes.
Uploads
Papers by Miklós Krész