Use this URL to cite or link to this record in EThOS:
Title: Approximation algorithms for packing and buffering problems
Author: Matsakis, Nicolaos
ISNI:       0000 0004 5992 622X
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2015
Availability of Full Text:
Access from EThOS:
Access from Institution:
This thesis studies online and offine approximation algorithms for packing and buffering problems. In the second chapter of this thesis, we study the problem of packing linear programs online. In this problem, the online algorithm may only increase the values of the variables of the linear program and his goal is to maximize the value of the objective function of it. The online algorithm has initially full knowledge of all parameters of the linear program, except for the right-hand sides of the constraints which are gradually revealed to him by the adversary. This online problem has been introduced by Ochel et al. [2012]. Our contribution (Englert et al. [2014]) is to provide improved upper bounds for the competitiveness of both deterministic and randomized online algorithms for this problem, as well as an optimal deterministic online algorithm for the special case of linear programs involving two variables. In the third chapter we study the offine COLORFUL BIN PACKING problem. This problem is a variant of the BIN PACKING problem, where each item is associated with a color and where there exists the additional restriction that two items packed consecutively into the same bin cannot share the same color. The COLORFUL BIN PACKING problem has been studied mainly from an online perspective and has been introduced as a generalization of the BLACK AND WHITE BIN PACKING problem (Balogh et al. [2012]), i.e., the special case of this problem for two colors. We provide (joint work with Matthias Englert) a 2-appoximate algorithm for the COLORFUL BIN PACKING problem. In the fourth chapter we study the Longest Queue Drop (LQD) online algorithm for shared-memory switches with three and two output ports. The Longest Queue Drop algorithm is a well-known online algorithm used to direct the packet ow of shared-memory switches. According to LQD, when the buffer of the switch becomes full, a packet is preempted from the longest queue in the buffer to free buffer space for the newly arriving packet which is accepted. We show (Matsakis [2016], to appear) that the Longest Queue Drop algorithm is (3/2)-competitive for three-port switches, improving the previously best upper bound of 5/3 (Kobayashi et al. [2007]). Additionally, we show that this algorithm is exactly (4/3)-competitive for two-port switches, correcting a previously published result claiming a tight upper bound of 4M-4/3M-2 < 4=3, where M 2 Z+ denotes the buffer size.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QA76 Electronic computers. Computer science. Computer software