@inproceedings{D'AndreagiovanniKrolikowskiPulaj, author = {D'Andreagiovanni, Fabio and Krolikowski, Jonatan and Pulaj, Jonad}, title = {A hybrid primal heuristic for Robust Multiperiod Network Design}, series = {EvoApplications 2014}, booktitle = {EvoApplications 2014}, language = {en} } @misc{D'AndreagiovanniKrolikowskiPulaj, author = {D'Andreagiovanni, Fabio and Krolikowski, Jonatan and Pulaj, Jonad}, title = {A hybrid primal heuristic for Robust Multiperiod Network Design}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-44081}, abstract = {We investigate the Robust Multiperiod Network Design Problem, a generalization of the classical Capacitated Network Design Problem that additionally considers multiple design periods and provides solutions protected against traffic uncertainty. Given the intrinsic difficulty of the problem, which proves challenging even for state-of-the art commercial solvers, we propose a hybrid primal heuristic based on the combination of ant colony optimization and an exact large neighborhood search. Computational experiments on a set of realistic instances from the SNDlib show that our heuristic can find solutions of extremely good quality with low optimality gap.}, language = {en} } @article{D'AndreagiovanniKrolikowskiPulaj, author = {D'Andreagiovanni, Fabio and Krolikowski, Jonatan and Pulaj, Jonad}, title = {A fast hybrid primal heuristic for multiband robust capacitated network design with multiple time periods}, series = {Applied Soft Computing}, volume = {26}, journal = {Applied Soft Computing}, doi = {10.1016/j.asoc.2014.10.016}, pages = {497 -- 507}, abstract = {We investigate the Robust Multiperiod Network Design Problem, a generalization of the Capacitated Network Design Problem (CNDP) that, besides establishing flow routing and network capacity installation as in a canonical CNDP, also considers a planning horizon made up of multiple time periods and protection against fluctuations in traffic volumes. As a remedy against traffic volume uncertainty, we propose a Robust Optimization model based on Multiband Robustness (B{\"u}sing and D'Andreagiovanni, 2012), a refinement of classical Gamma-Robustness by Bertsimas and Sim (2004) that uses a system of multiple deviation bands. Since the resulting optimization problem may prove very challenging even for instances of moderate size solved by a state-of-the-art optimization solver, we propose a hybrid primal heuristic that combines a randomized fixing strategy inspired by ant colony optimization and an exact large neighbourhood search. Computational experiments on a set of realistic instances from the SNDlib (2010) show that our original heuristic can run fast and produce solutions of extremely high quality associated with low optimality gaps.}, language = {en} } @article{D'AndreagiovanniMettNardinetal., author = {D'Andreagiovanni, Fabio and Mett, Fabian and Nardin, Antonella and Pulaj, Jonad}, title = {Integrating LP-guided variable fixing with MIP heuristics in the robust design of hybrid wired-wireless FTTx access networks}, series = {Applied Soft Computing}, volume = {61}, journal = {Applied Soft Computing}, doi = {10.1016/j.asoc.2017.07.018}, pages = {1074 -- 1087}, abstract = {This study investigates how to model and solve the problem of optimally designing FTTx telecommunications access networks integrating wired and wireless technologies, while taking into account the uncertainty of wireless signal propagation. We propose an original robust optimization model for the related robust 3-architecture Connected Facility Location problem, which includes additional variables and constraints to model wireless signal coverage represented through signal-to-interference ratios. Since the resulting robust problem can prove very challenging even for a modern state-of-the art optimization solver, we propose to solve it by an original primal heuristic that combines a probabilistic variable fixing procedure, guided by peculiar Linear Programming relaxations, with a Mixed Integer Programming heuristic, based on an exact very large neighborhood search. A numerical study carried out on a set of realistic instances show that our heuristic can find solutions of much higher quality than a state-of-the-art solver.}, language = {en} } @misc{D'AndreagiovanniMettPulaj, author = {D'Andreagiovanni, Fabio and Mett, Fabian and Pulaj, Jonad}, title = {An (MI)LP-based Primal Heuristic for 3-Architecture Connected Facility Location in Urban Access Network Design}, issn = {1438-0064}, doi = {10.1007/978-3-319-31204-0_19}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-57139}, abstract = {We investigate the 3-architecture Connected Facility Location Problem arising in the design of urban telecommunication access networks integrating wired and wireless technologies. We propose an original optimization model for the problem that includes additional variables and constraints to take into account wireless signal coverage represented through signal-to-interference ratios. Since the problem can prove very challenging even for modern state-of-the art optimization solvers, we propose to solve it by an original primal heuristic that combines a probabilistic fixing procedure, guided by peculiar Linear Programming relaxations, with an exact MIP heuristic, based on a very large neighborhood search. Computational experiments on a set of realistic instances show that our heuristic can find solutions associated with much lower optimality gaps than a state-of-the-art solver.}, language = {en} } @inproceedings{D'AndreagiovanniMettPulaj, author = {D'Andreagiovanni, Fabio and Mett, Fabian and Pulaj, Jonad}, title = {An (MI)LP-based Primal Heuristic for 3-Architecture Connected Facility Location in Urban Access Network Design}, series = {EvoApplications: European Conference on the Applications of Evolutionary Computation. Applications of Evolutionary Computation. 19th European Conference, EvoApplications 2016, Porto, Portugal, March 30 -- April 1, 2016, Proceedings, Part I}, volume = {9597}, booktitle = {EvoApplications: European Conference on the Applications of Evolutionary Computation. Applications of Evolutionary Computation. 19th European Conference, EvoApplications 2016, Porto, Portugal, March 30 -- April 1, 2016, Proceedings, Part I}, doi = {10.1007/978-3-319-31204-0_19}, pages = {283 -- 298}, abstract = {We investigate the 3-architecture Connected Facility Location Problem arising in the design of urban telecommunication access networks integrating wired and wireless technologies. We propose an original optimization model for the problem that includes additional variables and constraints to take into account wireless signal coverage represented through signal-to-interference ratios. Since the problem can prove very challenging even for modern state-of-the art optimization solvers, we propose to solve it by an original primal heuristic that combines a probabilistic fixing procedure, guided by peculiar Linear Programming relaxations, with an exact MIP heuristic, based on a very large neighborhood search. Computational experiments on a set of realistic instances show that our heuristic can find solutions associated with much lower optimality gaps than a state-of-the-art solver.}, language = {en} } @misc{PulajRaymondTheis, author = {Pulaj, Jonad and Raymond, Annie and Theis, Dirk}, title = {New Conjectures For Union-Closed Families}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-56804}, abstract = {The Frankl conjecture, also known as the union-closed sets conjecture, states that there exists an element in at least half of the sets of any (non-empty) union-closed family. From an optimization point of view, one could instead prove that 2a is an upper bound to the number of sets in a union-closed family with n elements where each element is in at most a sets, where a and n are non-negative integers. Formulating these problems as integer programs we observe that computed optimal values do not vary with n. We formalize these observations as conjectures, and show that they are not equivalent to the Frankl conjecture while still having wide-reaching implications if proven true. Finally, we partially prove the new conjectures and discuss possible approaches to solve them completely.}, language = {en} }