In the last 15 years periodic timetable problems have found much interest in the combinatorial optimization community. We will focus on the optimisation task to minimise a weighted sum of undesirable slack times. This problem can be formulated as a mixed integer linear problem, which for real world instances is hard to solve. This is mainly caused by the integer variables, the so-called modulo parameter. At first we will discuss some results on the polyhedral structure of the periodic timetable problem. These ideas allow to define a modulo simplex basic solution by calculating the basic variables from modulo equations. This leads to a modulo network simplex method, which iteratively improves the solution by changing the simplex basis.
@InProceedings{nachtigall_et_al:OASIcs.ATMOS.2008.1588, author = {Nachtigall, Karl and Opitz, Jens}, title = {{Solving Periodic Timetable Optimisation Problems by Modulo Simplex Calculations}}, booktitle = {8th Workshop on Algorithmic Approaches for Transportation Modeling, Optimization, and Systems (ATMOS'08)}, pages = {1--15}, series = {Open Access Series in Informatics (OASIcs)}, ISBN = {978-3-939897-07-1}, ISSN = {2190-6807}, year = {2008}, volume = {9}, editor = {Fischetti, Matteo and Widmayer, Peter}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2008.1588}, URN = {urn:nbn:de:0030-drops-15884}, doi = {10.4230/OASIcs.ATMOS.2008.1588}, annote = {Keywords: Periodic event scheduling problem, integer programming, modulo network simplex} }
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