Djordje Stakic | Faculty of Mathematics, University of Belgrade (original) (raw)

Papers by Djordje Stakic

Research paper thumbnail of Desenvolvimento profissional de professores - o exemplo do curso credenciado da Wikimedia Sérvia

Devido a seu papel social e importância, a vocação docente, apesar de ter sido depreciada e margi... more Devido a seu papel social e importância, a vocação docente, apesar de ter sido depreciada e marginalizada na Sérvia nas últimas décadas, ainda tem uma das funções de maior responsabilidade na administração de mudanças em prol do desenvolvimento. Num tempo de

Research paper thumbnail of General Variable Neighborhood Search for Scheduling Heterogeneous Vehicles in Agriculture

Lecture Notes in Computer Science, 2019

A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Het... more A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Heterogeneous Vehicles (VSP-HV), which arises from optimizing the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP-HV is to minimize the time required for daily transportation of sugar beet by heterogeneous vehicles under problem-specific constraints. General Variable Neighborhood Search (GVNS) is designed as a solution method for the considered problem. A computational study is conducted on the set of real-life instances, as well as on the set of generated instances of larger dimensions. A Mixed Integer Quadratically Constraint Programming (MIQCP) model is developed and used within commercial Lingo 17 solver to obtain optimal or feasible solutions for small-size real-life problem instances. Experimental results show that the proposed GVNS quickly reaches all known optimal solutions or improves the upper bounds of feasible solutions on small-size instances. On larger problem instances, for which Lingo 17 could not find feasible solutions, GVNS provided its best solutions for limited CPU time.

Research paper thumbnail of Wiki-Librarian: A Project to Train Librarians and Students to Work with Wikipedia

Infoteka, 2021

Wiki-librarian is a multiyear project to train librarians and students of librarianship and infor... more Wiki-librarian is a multiyear project to train librarians and students of librarianship and information science to use wiki tools, including writing articles on Wikipedia. The project has existed since the beginning of 2015, and the University Library "Svetozar Marković" and is logistically and financially supported by Wikimedia Serbia. The part of the project that deals with the training of librarians is officially accredited. Moreover, the project has expanded its scope to work with students, as well as with librarians outside the training process, through editathons, digitization of content, participation in other wiki activities such as 1Lib1Ref, Wikipedian in Residence. Project activities were presented at several conferences and partially in several publications. On the one hand, better awareness of librarians of wiki software IT capabilities as well as methods for improved presentation of their knowledge in the digital wiki environment are achieved by this project, while on the other hand these activities significantly increase the textual resources of Serbian Wikipedia and their quality.

Research paper thumbnail of Библиотеке и Википедија заједно на вебу: слободно знање за све

Research paper thumbnail of Multi-Objective Container Transport Optimization on Intermodal Networks Based on Mathematical Model

Second International Conference on Traffic and Transport Engineering (ICTTE), 2014

International container shipping is one of the most dynamic economic sectors of the last few year... more International container shipping is one of the most dynamic economic sectors of the last few years. In terms of value, global seaborne container trade is believed to account for approximately 60 percent of all world seaborne trade, and was valued at around 5.6 trillion U.S. dollars in 2010. Reflecting the sharp growth in world trade, global container traffic was 7 times higher in 2011 than in 1990. The global container trade increased by 4.7% in 2013 and by the end of 2014 it should reach 684 million TEU. The development of container transport in recent years marks a constant intention for increased cargo flows. This paper analyzed multi-objective container transport optimization on intermodal transportation networks from the Far East to Serbia through selected Mediterranean ports (Koper, Rijeka, Bar, Thessaloniki and Constanza) composed by two legs. First leg (ocean freight) observed the six world's largest container operators (Maersk Line, Mediterranean Shipping Company, CMA CGM, Evergreen Line, China Ocean Shipping Company and Hapag-Lloyd) with theirs different types of services. The second leg of the chain represents the inland component of the distribution, in which containers are routed from gateways to a final destination, by road, rail or barge. The research used an evolutionary multi-objective mathematical model. The model observed multi-objective optimization, minimizing transportation cost, transit time and emissions. Inclusion of more objectives into the model results in obtaining accurate information to the observed objects at the same time. Cost and transit time are the two most common considerations in transport planning problems. Results provide an optimal route with shortest transit time, lowest transportation cost and minimum of emissions between the Far East and Serbia and give the authors the possibility of observing the group of all possible solutions, which are ranked in ascending order.

Research paper thumbnail of Variable neighborhood search for optimizing the transportation of agricultural raw materials

Electronic Notes in Discrete Mathematics, Apr 1, 2017

Low price of raw materials in sugar industry and characteristics of production method lead to the... more Low price of raw materials in sugar industry and characteristics of production method lead to the specific transport organization problem. A new variant of Vehicle Scheduling Problem (VSP) that arises from transportation of sugar beet is considered. The problem is formulated as a Mixed Integer Quadratically Constraint Programming (MIQCP) model, which reflects the objective and specific constrains from practice. Computational experiments are conducted on real-life instances obtained from a sugar company in Serbia and the set of generated instances of larger dimensions. The proposed MIQCP model is used within the framework of Extended Lingo 15 solver, providing optimal solutions on smallsize instances only. In order to find solutions on larger problem instances, a metaheuristic method based on Variable Neighborhood Search (VNS) is designed. Obtained computational results show that the proposed VNS quickly reaches all known optimal solutions on small-size instances. On larger problem instances, for which Lingo 15 solver could not find even a feasible solution, VNS provides best solutions in relatively short running times.

Research paper thumbnail of Variable neighborhood search based approaches to a vehicle scheduling problem in agriculture

International Transactions in Operational Research, Dec 1, 2017

A vehicle scheduling problem (VSP) that arises from sugar beet transportation within minimum work... more A vehicle scheduling problem (VSP) that arises from sugar beet transportation within minimum working time under the set of constraints reflecting a real-life situation is considered. A mixed integer quadratically constrained programming (MIQCP) model of the considered VSP and reformulation to a mixed integer linear program (MILP) are proposed and used within the framework of Lingo 17 solver, producing optimal solutions only for small-sized problem instances. Two variants of the variable neighborhood search (VNS) metaheuristic-basic VNS (BVNS) and skewed VNS (SVNS) are designed to efficiently deal with large-sized problem instances. The proposed VNS approaches are evaluated and compared against Lingo 17 and each other on the set of real-life and generated problem instances. Computational results show that both BVNS and SVNS reach all known optimal solutions on small-sized instances and are comparable on medium-and large-sized instances. In general, SVNS significantly outperforms BVNS in terms of running times.

Research paper thumbnail of A Reduced Variable Neighborhood Search Approach to the Heterogeneous Vector Bin Packing Problem

Information Technology and Control, Dec 16, 2021

The two-dimensional heterogeneous vector bin packing problem (2DHet-VBPP) consists of packing the... more The two-dimensional heterogeneous vector bin packing problem (2DHet-VBPP) consists of packing the set of items into the set of various type bins, respecting their two resource limits. The problem is to minimize the total cost of all bins. The problem, known to be NP-hard, can be formulated as a pure integer linear program, but optimal solutions can be obtained by the CPLEX Optimizer engine only for small instances. This paper proposes a metaheuristic approach to the 2DHet-VBPP, based on Reduced variable neighborhood search (RVNS). All RVNS elements are adapted to the considered problem and many procedures are designed to improve efficiency of the method. As the Two-dimensional Homogeneous-VBPP (2DHom-VBPP) is more often treated, we considered also a special version of the RVNS algorithm to solve the 2DHom-VBPP. The results obtained and compared to both CPLEX results and results on benchmark instances from literature, justify the use of the RVNS algorithm to solve large instances of these optimization problems.

Research paper thumbnail of Metaheuristic approaches to a vehicle scheduling problem in sugar beet transportation

Operational Research, May 31, 2019

A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sug... more A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP is to minimize the required transportation time under problem-specific constraints. The problem is formulated as a mixed integer linear program (MILP). Within the framework of commercial CPLEX solver the proposed MILP model was able to produce optimal solutions for small size problem instances. Therefore, two metaheuristic methods, variable neighborhood search (VNS) and greedy randomized adaptive search procedure (GRASP), are designed to solve problem instances of larger dimensions. The proposed GRASP and VNS are evaluated and compared against CPLEX and each other on the set of real-life and generated problem instances. Computational results show that VNS is superior method with respect to the solution quality, while GRASP is able to find high quality solutions within very short running times.

Research paper thumbnail of Students’ Attitudes Towards the Use of Wikipedia: A Teaching Tool and a Way to Modernize Teaching

Área abierta, May 17, 2021

This paper presents a research on students' attitudes towards the use of Wikipedia in teaching. T... more This paper presents a research on students' attitudes towards the use of Wikipedia in teaching. The sample was comprised of students from the Pedagogical Faculty in Vranje, a higher education institution affiliated with the University of Niš, Serbia. Students were assigned to write articles on Wikipedia as an alternative to writing their standard term papers; this way the Wikipedia content became significantly enriched, positively evaluating the website as a teaching tool in the process. The results confirmed that students preferred creating articles on Wikipedia to writing standard term papers. Those results may contribute significantly to further improvement and modernization of university teaching.

Research paper thumbnail of Role of Cargo Weight and Volume: Minimizing Costs and CO2 Emissions in Container Transport

Commercial Transport, 2015

The container revolution has resulted in major changes in international trade and it is the one o... more The container revolution has resulted in major changes in international trade and it is the one of the most important contributions to the globalization of the world economy. In addition to an increased coordination and cooperation between different forms of transport, containerization offers benefits in form of direct effects on cost-reduction and acceleration of the “door to door” cargo distribution process, which is of crucial importance to transport users. In a constant exchange of goods between buyers and sellers around the world, goods of various type and different size and weight are transported. In most logistics systems, minimization of costs has always been the main objective. This paper departs from the previous approaches and includes the study of carbon dioxide (CO2) emissions, taking into consideration the beneficial impact of their reduction and quality analysis on sustainability of ecosystems. A bi-objective mathematical model is proposed, aimed at minimizing container transportation costs and CO2 emissions. This paper analyzes an intermodal transportation chain, based on the import-way and composed of two legs. The intermodal transportation network is composed of three categories of nodes—origin port, gateway ports and destination, and two link categories—maritime and inland. Furthermore, the inclusion of additional objectives into the model enables obtaining more accurate information of the observed objects. The transportation costs were considered for each of the most-commonly used types of containers in container transport, depending on different cargo volume and weight. The total CO2 emissions include ocean transport emissions from container ships and land emissions produced by truck and rail. The model was programmed in MATLAB. The bi-objective optimization has been analyzed by use of different carbon footprint factors for different modes of transport. The developed mathematical model offers a broad range of possible solutions and provides a possibility of their ranking and selecting the most optimal solution, with respect to minimization of transportation costs and CO2 emissions. The advantage of this model is its broad applicability to various ‘point to point’ relations, in which containers are transported by combination of sea and land. The model application enables obtaining adequate and reliable solutions to the observed problem. The combination of the modelling approach and the methods used is novel and with appropriate input parameters enables accurate results in logistic networks.

Research paper thumbnail of Primjena matematičkog modela za kontejnerske tokove robe: s Dalekog istoka ka Srbiji

Tehnicki Vjesnik-technical Gazette, Nov 29, 2016

Original scientific paper Container transport represents a key component of intermodal transport ... more Original scientific paper Container transport represents a key component of intermodal transport and a substantial contribution to the rapidly growing international trade. The container trade should be optimal to provide a suitable resource utilisation and profitability to key operators, providing them an easy and relatively cheap access to international markets. Numerous algorithms have been generated to provide an efficient solution to optimisation problems in container trade. This paper analyses the supply-chain network focusing on container import from the Far East to Serbia through selected Mediterranean ports (Koper, Rijeka, Bar, Thessaloniki and Constanta). An optimisation mathematical model was developed, minimising the transit time and transportation costs of container imports to Serbia, by means of using various liner shipping services on the deep-short sea and truck-rail-barge inland transport networks from selected ports. By using the bi-objective model for container flows from the Far East through Mediterranean ports, the optimal path for container import to Serbia has been determined. Certain groups of customers require the lowest freight rates, while others give priority to a faster delivery.

Research paper thumbnail of Comparison of Different Grasp Algorithms for the Heterogeneous Vector Bin Packing Problem

2019 China-Qatar International Workshop on Artificial Intelligence and Applications to Intelligent Manufacturing (AIAIM), 2019

In this paper, we address the practical problem of packing multiple items into containers for fur... more In this paper, we address the practical problem of packing multiple items into containers for further transport. Dense packing of containers can significantly decrease supply chain costs, since transport fees are related to the the number of used containers and not the content. This practical problem is generally modeled using the vector bin packing problem (VBPP) and its variations. In the recent years, the heterogeneous VBPP with two sets of constraints has proven to be a good representation of container packing related problems. In this work we extend this model to a more realistic setting, by allowing multiple containers of the same type. To solve this problem, an integer program is designed. To be able to find feasible solutions for large scale problem instances, a greedy constructive algorithm is developed. With the intention of improving the solutions generated in this way, a local search is developed and used to extend the greedy algorithm to the Greedy Randomized Adaptive S...

Research paper thumbnail of General Variable Neighborhood Search for Scheduling Heterogeneous Vehicles in Agriculture

A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Het... more A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Heterogeneous Vehicles (VSP-HV), which arises from optimizing the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP-HV is to minimize the time required for daily transportation of sugar beet by heterogeneous vehicles under problem-specific constraints. General Variable Neighborhood Search (GVNS) is designed as a solution method for the considered problem. A computational study is conducted on the set of real-life instances, as well as on the set of generated instances of larger dimensions. A Mixed Integer Quadratically Constraint Programming (MIQCP) model is developed and used within commercial Lingo 17 solver to obtain optimal or feasible solutions for small-size real-life problem instances. Experimental results show that the proposed GVNS quickly reaches all known optimal solutions or improves the upper bounds of feasible solutions o...

Research paper thumbnail of Metaheuristic approaches to a vehicle scheduling problem in sugar beet transportation

Operational Research, 2019

A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sug... more A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP is to minimize the required transportation time under problem-specific constraints. The problem is formulated as a mixed integer linear program (MILP). Within the framework of commercial CPLEX solver the proposed MILP model was able to produce optimal solutions for small size problem instances. Therefore, two metaheuristic methods, variable neighborhood search (VNS) and greedy randomized adaptive search procedure (GRASP), are designed to solve problem instances of larger dimensions. The proposed GRASP and VNS are evaluated and compared against CPLEX and each other on the set of real-life and generated problem instances. Computational results show that VNS is superior method with respect to the solution quality, while GRASP is able to find high quality solutions within very short running times.

Research paper thumbnail of Primjena matematičkog modela za kontejnerske tokove robe: s Dalekog istoka ka Srbiji

Tehnicki Vjesnik-technical Gazette, Nov 29, 2016

Research paper thumbnail of Comparison of Different Grasp Algorithms for the Heterogeneous Vector Bin Packing Problem

2019 China-Qatar International Workshop on Artificial Intelligence and Applications to Intelligent Manufacturing (AIAIM), 2019

In this paper, we address the practical problem of packing multiple items into containers for fur... more In this paper, we address the practical problem of packing multiple items into containers for further transport. Dense packing of containers can significantly decrease supply chain costs, since transport fees are related to the the number of used containers and not the content. This practical problem is generally modeled using the vector bin packing problem (VBPP) and its variations. In the recent years, the heterogeneous VBPP with two sets of constraints has proven to be a good representation of container packing related problems. In this work we extend this model to a more realistic setting, by allowing multiple containers of the same type. To solve this problem, an integer program is designed. To be able to find feasible solutions for large scale problem instances, a greedy constructive algorithm is developed. With the intention of improving the solutions generated in this way, a local search is developed and used to extend the greedy algorithm to the Greedy Randomized Adaptive S...

Research paper thumbnail of General Variable Neighborhood Search for Scheduling Heterogeneous Vehicles in Agriculture

A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Het... more A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Heterogeneous Vehicles (VSP-HV), which arises from optimizing the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP-HV is to minimize the time required for daily transportation of sugar beet by heterogeneous vehicles under problem-specific constraints. General Variable Neighborhood Search (GVNS) is designed as a solution method for the considered problem. A computational study is conducted on the set of real-life instances, as well as on the set of generated instances of larger dimensions. A Mixed Integer Quadratically Constraint Programming (MIQCP) model is developed and used within commercial Lingo 17 solver to obtain optimal or feasible solutions for small-size real-life problem instances. Experimental results show that the proposed GVNS quickly reaches all known optimal solutions or improves the upper bounds of feasible solutions o...

Research paper thumbnail of Metaheuristic approaches to a vehicle scheduling problem in sugar beet transportation

Operational Research, 2019

A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sug... more A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP is to minimize the required transportation time under problem-specific constraints. The problem is formulated as a mixed integer linear program (MILP). Within the framework of commercial CPLEX solver the proposed MILP model was able to produce optimal solutions for small size problem instances. Therefore, two metaheuristic methods, variable neighborhood search (VNS) and greedy randomized adaptive search procedure (GRASP), are designed to solve problem instances of larger dimensions. The proposed GRASP and VNS are evaluated and compared against CPLEX and each other on the set of real-life and generated problem instances. Computational results show that VNS is superior method with respect to the solution quality, while GRASP is able to find high quality solutions within very short running times.

Research paper thumbnail of Variable neighborhood search based approaches to a vehicle scheduling problem in agriculture

International Transactions in Operational Research, 2017

A vehicle scheduling problem (VSP) that arises from sugar beet transportation within minimum work... more A vehicle scheduling problem (VSP) that arises from sugar beet transportation within minimum working time under the set of constraints reflecting a real-life situation is considered. A mixed integer quadratically constrained programming (MIQCP) model of the considered VSP and reformulation to a mixed integer linear program (MILP) are proposed and used within the framework of Lingo 17 solver, producing optimal solutions only for small-sized problem instances. Two variants of the variable neighborhood search (VNS) metaheuristic-basic VNS (BVNS) and skewed VNS (SVNS) are designed to efficiently deal with large-sized problem instances. The proposed VNS approaches are evaluated and compared against Lingo 17 and each other on the set of real-life and generated problem instances. Computational results show that both BVNS and SVNS reach all known optimal solutions on small-sized instances and are comparable on medium-and large-sized instances. In general, SVNS significantly outperforms BVNS in terms of running times.

Research paper thumbnail of Desenvolvimento profissional de professores - o exemplo do curso credenciado da Wikimedia Sérvia

Devido a seu papel social e importância, a vocação docente, apesar de ter sido depreciada e margi... more Devido a seu papel social e importância, a vocação docente, apesar de ter sido depreciada e marginalizada na Sérvia nas últimas décadas, ainda tem uma das funções de maior responsabilidade na administração de mudanças em prol do desenvolvimento. Num tempo de

Research paper thumbnail of General Variable Neighborhood Search for Scheduling Heterogeneous Vehicles in Agriculture

Lecture Notes in Computer Science, 2019

A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Het... more A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Heterogeneous Vehicles (VSP-HV), which arises from optimizing the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP-HV is to minimize the time required for daily transportation of sugar beet by heterogeneous vehicles under problem-specific constraints. General Variable Neighborhood Search (GVNS) is designed as a solution method for the considered problem. A computational study is conducted on the set of real-life instances, as well as on the set of generated instances of larger dimensions. A Mixed Integer Quadratically Constraint Programming (MIQCP) model is developed and used within commercial Lingo 17 solver to obtain optimal or feasible solutions for small-size real-life problem instances. Experimental results show that the proposed GVNS quickly reaches all known optimal solutions or improves the upper bounds of feasible solutions on small-size instances. On larger problem instances, for which Lingo 17 could not find feasible solutions, GVNS provided its best solutions for limited CPU time.

Research paper thumbnail of Wiki-Librarian: A Project to Train Librarians and Students to Work with Wikipedia

Infoteka, 2021

Wiki-librarian is a multiyear project to train librarians and students of librarianship and infor... more Wiki-librarian is a multiyear project to train librarians and students of librarianship and information science to use wiki tools, including writing articles on Wikipedia. The project has existed since the beginning of 2015, and the University Library "Svetozar Marković" and is logistically and financially supported by Wikimedia Serbia. The part of the project that deals with the training of librarians is officially accredited. Moreover, the project has expanded its scope to work with students, as well as with librarians outside the training process, through editathons, digitization of content, participation in other wiki activities such as 1Lib1Ref, Wikipedian in Residence. Project activities were presented at several conferences and partially in several publications. On the one hand, better awareness of librarians of wiki software IT capabilities as well as methods for improved presentation of their knowledge in the digital wiki environment are achieved by this project, while on the other hand these activities significantly increase the textual resources of Serbian Wikipedia and their quality.

Research paper thumbnail of Библиотеке и Википедија заједно на вебу: слободно знање за све

Research paper thumbnail of Multi-Objective Container Transport Optimization on Intermodal Networks Based on Mathematical Model

Second International Conference on Traffic and Transport Engineering (ICTTE), 2014

International container shipping is one of the most dynamic economic sectors of the last few year... more International container shipping is one of the most dynamic economic sectors of the last few years. In terms of value, global seaborne container trade is believed to account for approximately 60 percent of all world seaborne trade, and was valued at around 5.6 trillion U.S. dollars in 2010. Reflecting the sharp growth in world trade, global container traffic was 7 times higher in 2011 than in 1990. The global container trade increased by 4.7% in 2013 and by the end of 2014 it should reach 684 million TEU. The development of container transport in recent years marks a constant intention for increased cargo flows. This paper analyzed multi-objective container transport optimization on intermodal transportation networks from the Far East to Serbia through selected Mediterranean ports (Koper, Rijeka, Bar, Thessaloniki and Constanza) composed by two legs. First leg (ocean freight) observed the six world's largest container operators (Maersk Line, Mediterranean Shipping Company, CMA CGM, Evergreen Line, China Ocean Shipping Company and Hapag-Lloyd) with theirs different types of services. The second leg of the chain represents the inland component of the distribution, in which containers are routed from gateways to a final destination, by road, rail or barge. The research used an evolutionary multi-objective mathematical model. The model observed multi-objective optimization, minimizing transportation cost, transit time and emissions. Inclusion of more objectives into the model results in obtaining accurate information to the observed objects at the same time. Cost and transit time are the two most common considerations in transport planning problems. Results provide an optimal route with shortest transit time, lowest transportation cost and minimum of emissions between the Far East and Serbia and give the authors the possibility of observing the group of all possible solutions, which are ranked in ascending order.

Research paper thumbnail of Variable neighborhood search for optimizing the transportation of agricultural raw materials

Electronic Notes in Discrete Mathematics, Apr 1, 2017

Low price of raw materials in sugar industry and characteristics of production method lead to the... more Low price of raw materials in sugar industry and characteristics of production method lead to the specific transport organization problem. A new variant of Vehicle Scheduling Problem (VSP) that arises from transportation of sugar beet is considered. The problem is formulated as a Mixed Integer Quadratically Constraint Programming (MIQCP) model, which reflects the objective and specific constrains from practice. Computational experiments are conducted on real-life instances obtained from a sugar company in Serbia and the set of generated instances of larger dimensions. The proposed MIQCP model is used within the framework of Extended Lingo 15 solver, providing optimal solutions on smallsize instances only. In order to find solutions on larger problem instances, a metaheuristic method based on Variable Neighborhood Search (VNS) is designed. Obtained computational results show that the proposed VNS quickly reaches all known optimal solutions on small-size instances. On larger problem instances, for which Lingo 15 solver could not find even a feasible solution, VNS provides best solutions in relatively short running times.

Research paper thumbnail of Variable neighborhood search based approaches to a vehicle scheduling problem in agriculture

International Transactions in Operational Research, Dec 1, 2017

A vehicle scheduling problem (VSP) that arises from sugar beet transportation within minimum work... more A vehicle scheduling problem (VSP) that arises from sugar beet transportation within minimum working time under the set of constraints reflecting a real-life situation is considered. A mixed integer quadratically constrained programming (MIQCP) model of the considered VSP and reformulation to a mixed integer linear program (MILP) are proposed and used within the framework of Lingo 17 solver, producing optimal solutions only for small-sized problem instances. Two variants of the variable neighborhood search (VNS) metaheuristic-basic VNS (BVNS) and skewed VNS (SVNS) are designed to efficiently deal with large-sized problem instances. The proposed VNS approaches are evaluated and compared against Lingo 17 and each other on the set of real-life and generated problem instances. Computational results show that both BVNS and SVNS reach all known optimal solutions on small-sized instances and are comparable on medium-and large-sized instances. In general, SVNS significantly outperforms BVNS in terms of running times.

Research paper thumbnail of A Reduced Variable Neighborhood Search Approach to the Heterogeneous Vector Bin Packing Problem

Information Technology and Control, Dec 16, 2021

The two-dimensional heterogeneous vector bin packing problem (2DHet-VBPP) consists of packing the... more The two-dimensional heterogeneous vector bin packing problem (2DHet-VBPP) consists of packing the set of items into the set of various type bins, respecting their two resource limits. The problem is to minimize the total cost of all bins. The problem, known to be NP-hard, can be formulated as a pure integer linear program, but optimal solutions can be obtained by the CPLEX Optimizer engine only for small instances. This paper proposes a metaheuristic approach to the 2DHet-VBPP, based on Reduced variable neighborhood search (RVNS). All RVNS elements are adapted to the considered problem and many procedures are designed to improve efficiency of the method. As the Two-dimensional Homogeneous-VBPP (2DHom-VBPP) is more often treated, we considered also a special version of the RVNS algorithm to solve the 2DHom-VBPP. The results obtained and compared to both CPLEX results and results on benchmark instances from literature, justify the use of the RVNS algorithm to solve large instances of these optimization problems.

Research paper thumbnail of Metaheuristic approaches to a vehicle scheduling problem in sugar beet transportation

Operational Research, May 31, 2019

A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sug... more A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP is to minimize the required transportation time under problem-specific constraints. The problem is formulated as a mixed integer linear program (MILP). Within the framework of commercial CPLEX solver the proposed MILP model was able to produce optimal solutions for small size problem instances. Therefore, two metaheuristic methods, variable neighborhood search (VNS) and greedy randomized adaptive search procedure (GRASP), are designed to solve problem instances of larger dimensions. The proposed GRASP and VNS are evaluated and compared against CPLEX and each other on the set of real-life and generated problem instances. Computational results show that VNS is superior method with respect to the solution quality, while GRASP is able to find high quality solutions within very short running times.

Research paper thumbnail of Students’ Attitudes Towards the Use of Wikipedia: A Teaching Tool and a Way to Modernize Teaching

Área abierta, May 17, 2021

This paper presents a research on students' attitudes towards the use of Wikipedia in teaching. T... more This paper presents a research on students' attitudes towards the use of Wikipedia in teaching. The sample was comprised of students from the Pedagogical Faculty in Vranje, a higher education institution affiliated with the University of Niš, Serbia. Students were assigned to write articles on Wikipedia as an alternative to writing their standard term papers; this way the Wikipedia content became significantly enriched, positively evaluating the website as a teaching tool in the process. The results confirmed that students preferred creating articles on Wikipedia to writing standard term papers. Those results may contribute significantly to further improvement and modernization of university teaching.

Research paper thumbnail of Role of Cargo Weight and Volume: Minimizing Costs and CO2 Emissions in Container Transport

Commercial Transport, 2015

The container revolution has resulted in major changes in international trade and it is the one o... more The container revolution has resulted in major changes in international trade and it is the one of the most important contributions to the globalization of the world economy. In addition to an increased coordination and cooperation between different forms of transport, containerization offers benefits in form of direct effects on cost-reduction and acceleration of the “door to door” cargo distribution process, which is of crucial importance to transport users. In a constant exchange of goods between buyers and sellers around the world, goods of various type and different size and weight are transported. In most logistics systems, minimization of costs has always been the main objective. This paper departs from the previous approaches and includes the study of carbon dioxide (CO2) emissions, taking into consideration the beneficial impact of their reduction and quality analysis on sustainability of ecosystems. A bi-objective mathematical model is proposed, aimed at minimizing container transportation costs and CO2 emissions. This paper analyzes an intermodal transportation chain, based on the import-way and composed of two legs. The intermodal transportation network is composed of three categories of nodes—origin port, gateway ports and destination, and two link categories—maritime and inland. Furthermore, the inclusion of additional objectives into the model enables obtaining more accurate information of the observed objects. The transportation costs were considered for each of the most-commonly used types of containers in container transport, depending on different cargo volume and weight. The total CO2 emissions include ocean transport emissions from container ships and land emissions produced by truck and rail. The model was programmed in MATLAB. The bi-objective optimization has been analyzed by use of different carbon footprint factors for different modes of transport. The developed mathematical model offers a broad range of possible solutions and provides a possibility of their ranking and selecting the most optimal solution, with respect to minimization of transportation costs and CO2 emissions. The advantage of this model is its broad applicability to various ‘point to point’ relations, in which containers are transported by combination of sea and land. The model application enables obtaining adequate and reliable solutions to the observed problem. The combination of the modelling approach and the methods used is novel and with appropriate input parameters enables accurate results in logistic networks.

Research paper thumbnail of Primjena matematičkog modela za kontejnerske tokove robe: s Dalekog istoka ka Srbiji

Tehnicki Vjesnik-technical Gazette, Nov 29, 2016

Original scientific paper Container transport represents a key component of intermodal transport ... more Original scientific paper Container transport represents a key component of intermodal transport and a substantial contribution to the rapidly growing international trade. The container trade should be optimal to provide a suitable resource utilisation and profitability to key operators, providing them an easy and relatively cheap access to international markets. Numerous algorithms have been generated to provide an efficient solution to optimisation problems in container trade. This paper analyses the supply-chain network focusing on container import from the Far East to Serbia through selected Mediterranean ports (Koper, Rijeka, Bar, Thessaloniki and Constanta). An optimisation mathematical model was developed, minimising the transit time and transportation costs of container imports to Serbia, by means of using various liner shipping services on the deep-short sea and truck-rail-barge inland transport networks from selected ports. By using the bi-objective model for container flows from the Far East through Mediterranean ports, the optimal path for container import to Serbia has been determined. Certain groups of customers require the lowest freight rates, while others give priority to a faster delivery.

Research paper thumbnail of Comparison of Different Grasp Algorithms for the Heterogeneous Vector Bin Packing Problem

2019 China-Qatar International Workshop on Artificial Intelligence and Applications to Intelligent Manufacturing (AIAIM), 2019

In this paper, we address the practical problem of packing multiple items into containers for fur... more In this paper, we address the practical problem of packing multiple items into containers for further transport. Dense packing of containers can significantly decrease supply chain costs, since transport fees are related to the the number of used containers and not the content. This practical problem is generally modeled using the vector bin packing problem (VBPP) and its variations. In the recent years, the heterogeneous VBPP with two sets of constraints has proven to be a good representation of container packing related problems. In this work we extend this model to a more realistic setting, by allowing multiple containers of the same type. To solve this problem, an integer program is designed. To be able to find feasible solutions for large scale problem instances, a greedy constructive algorithm is developed. With the intention of improving the solutions generated in this way, a local search is developed and used to extend the greedy algorithm to the Greedy Randomized Adaptive S...

Research paper thumbnail of General Variable Neighborhood Search for Scheduling Heterogeneous Vehicles in Agriculture

A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Het... more A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Heterogeneous Vehicles (VSP-HV), which arises from optimizing the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP-HV is to minimize the time required for daily transportation of sugar beet by heterogeneous vehicles under problem-specific constraints. General Variable Neighborhood Search (GVNS) is designed as a solution method for the considered problem. A computational study is conducted on the set of real-life instances, as well as on the set of generated instances of larger dimensions. A Mixed Integer Quadratically Constraint Programming (MIQCP) model is developed and used within commercial Lingo 17 solver to obtain optimal or feasible solutions for small-size real-life problem instances. Experimental results show that the proposed GVNS quickly reaches all known optimal solutions or improves the upper bounds of feasible solutions o...

Research paper thumbnail of Metaheuristic approaches to a vehicle scheduling problem in sugar beet transportation

Operational Research, 2019

A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sug... more A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP is to minimize the required transportation time under problem-specific constraints. The problem is formulated as a mixed integer linear program (MILP). Within the framework of commercial CPLEX solver the proposed MILP model was able to produce optimal solutions for small size problem instances. Therefore, two metaheuristic methods, variable neighborhood search (VNS) and greedy randomized adaptive search procedure (GRASP), are designed to solve problem instances of larger dimensions. The proposed GRASP and VNS are evaluated and compared against CPLEX and each other on the set of real-life and generated problem instances. Computational results show that VNS is superior method with respect to the solution quality, while GRASP is able to find high quality solutions within very short running times.

Research paper thumbnail of Primjena matematičkog modela za kontejnerske tokove robe: s Dalekog istoka ka Srbiji

Tehnicki Vjesnik-technical Gazette, Nov 29, 2016

Research paper thumbnail of Comparison of Different Grasp Algorithms for the Heterogeneous Vector Bin Packing Problem

2019 China-Qatar International Workshop on Artificial Intelligence and Applications to Intelligent Manufacturing (AIAIM), 2019

In this paper, we address the practical problem of packing multiple items into containers for fur... more In this paper, we address the practical problem of packing multiple items into containers for further transport. Dense packing of containers can significantly decrease supply chain costs, since transport fees are related to the the number of used containers and not the content. This practical problem is generally modeled using the vector bin packing problem (VBPP) and its variations. In the recent years, the heterogeneous VBPP with two sets of constraints has proven to be a good representation of container packing related problems. In this work we extend this model to a more realistic setting, by allowing multiple containers of the same type. To solve this problem, an integer program is designed. To be able to find feasible solutions for large scale problem instances, a greedy constructive algorithm is developed. With the intention of improving the solutions generated in this way, a local search is developed and used to extend the greedy algorithm to the Greedy Randomized Adaptive S...

Research paper thumbnail of General Variable Neighborhood Search for Scheduling Heterogeneous Vehicles in Agriculture

A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Het... more A new variant of Vehicle Scheduling Problem (VSP), denoted as Vehicle Scheduling Problem with Heterogeneous Vehicles (VSP-HV), which arises from optimizing the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP-HV is to minimize the time required for daily transportation of sugar beet by heterogeneous vehicles under problem-specific constraints. General Variable Neighborhood Search (GVNS) is designed as a solution method for the considered problem. A computational study is conducted on the set of real-life instances, as well as on the set of generated instances of larger dimensions. A Mixed Integer Quadratically Constraint Programming (MIQCP) model is developed and used within commercial Lingo 17 solver to obtain optimal or feasible solutions for small-size real-life problem instances. Experimental results show that the proposed GVNS quickly reaches all known optimal solutions or improves the upper bounds of feasible solutions o...

Research paper thumbnail of Metaheuristic approaches to a vehicle scheduling problem in sugar beet transportation

Operational Research, 2019

A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sug... more A variant of vehicle scheduling problem (VSP) arising from the sugar beet transportation in a sugar factory in Serbia is introduced. The objective of the considered VSP is to minimize the required transportation time under problem-specific constraints. The problem is formulated as a mixed integer linear program (MILP). Within the framework of commercial CPLEX solver the proposed MILP model was able to produce optimal solutions for small size problem instances. Therefore, two metaheuristic methods, variable neighborhood search (VNS) and greedy randomized adaptive search procedure (GRASP), are designed to solve problem instances of larger dimensions. The proposed GRASP and VNS are evaluated and compared against CPLEX and each other on the set of real-life and generated problem instances. Computational results show that VNS is superior method with respect to the solution quality, while GRASP is able to find high quality solutions within very short running times.

Research paper thumbnail of Variable neighborhood search based approaches to a vehicle scheduling problem in agriculture

International Transactions in Operational Research, 2017

A vehicle scheduling problem (VSP) that arises from sugar beet transportation within minimum work... more A vehicle scheduling problem (VSP) that arises from sugar beet transportation within minimum working time under the set of constraints reflecting a real-life situation is considered. A mixed integer quadratically constrained programming (MIQCP) model of the considered VSP and reformulation to a mixed integer linear program (MILP) are proposed and used within the framework of Lingo 17 solver, producing optimal solutions only for small-sized problem instances. Two variants of the variable neighborhood search (VNS) metaheuristic-basic VNS (BVNS) and skewed VNS (SVNS) are designed to efficiently deal with large-sized problem instances. The proposed VNS approaches are evaluated and compared against Lingo 17 and each other on the set of real-life and generated problem instances. Computational results show that both BVNS and SVNS reach all known optimal solutions on small-sized instances and are comparable on medium-and large-sized instances. In general, SVNS significantly outperforms BVNS in terms of running times.