Date  Speaker  Title and Abstract 
July 12th
*Thursday* *2:004:30* *SUR 2980* 
Pooja Pandey
Ph.D. thesis defence Senior Supervisor: A. Punnen 
Topics in Quadratic Binary Optimization Problems
Abstract: In this dissertation, we consider the quadratic combinatorial optimization problem (QCOP) and its variations: the generalized vertex cover problem (GVC), the quadratic unconstrained binary optimization problem (QUBO), and the quadratic set covering problem (QSCP). We study these problems as discussed below. For QCOP, we analyze equivalent representations of the pair (Q, c), where Q is a quadratic cost matrix and c is a linear cost vector. We present various procedures to obtain equivalent representations, and study the effect of equivalent representations on the computation time to obtain an optimal solution, on the quality of the lower bound values obtained by various lower bounding schemes, and on the quality of the heuristic solution. The first variation of QCOP is GVC, and we show that GVC is equivalent to QUBO and also equivalent to some other variations of GVC. Some solvable cases are identified and approximation algorithms are suggested for special cases. We also study GVC on bipartite graphs. QUBO is the second variation of QCOP. For QUBO, we analyze several heuristic algorithms using domination analysis. We show that for QUBO, if any algorithm that guarantees a solution no worse than the average, has a domination ratio of at least 1/40. We extend this result to the maximum and minimum cut problems; maximum and minimum uncut problems; and GVC. We also study the QUBO when Q is: 1) (2d + 1)diagonal matrix, 2) (2d + 1)reversediagonal matrix, and 3) (2d+1)cross diagonal matrix, and show that these cases are solvable in polynomial time when d is fixed or is of O(log n). The last variation of QCOP is QSCP. For QSCP, we identify various inaccuracies in the paper by R. R. Saxena and S. R. Arora, A linearization technique for solving the Quadratic Set Covering Problem, Optimization, 39 (1997) 3342. In particular, we observe that their algorithm does not guarantee optimality, contrary to what is claimed. We also present the mixed integer linear programming formulations (MILP) for QSCP. We compare the lower bounds obtained by the linear programming relaxations of MILPs, and study the effect of equivalent representations of QSCP on these MILPs. 
July 12th
*Thursday* *10:0012:30* *SUR 2710* 
Brad Woods
Ph.D. thesis defence Senior Supervisor: A. Punnen 
The Quadratic Travelling Salesman Problem:
Complexity and Approximation
Abstract: In this thesis we study the Quadratic Travelling Salesman Problem (QTSP) which generalizes the wellstudied Traveling Salesman Problem and several of its variations. QTSP is to find a least cost Hamiltonian cycle in an edgeweighted graph, where costs are defined for all pairs of edges contained in the Hamilton cycle. This is a more general version than the one that appears in the literature as the QTSP, denoted here as the adjacent quadratic TSP, which only considers costs for pairs of adjacent edges. The fixedrank QTSP is introduced as a restricted version of the QTSP where the cost matrix has fixed rank p. When c = 0, it is referred to as the homogenous rank p QTSP. We study QTSP by examining the complexity of searching exponential neighbourhoods for QTSP, the fixedrank QTSP and the adjacent quadratic TSP. 
May 10th
*2:30* via COCANA (Kelowna) 
Björn Rüffer
University of Newcastle (Australia) 
Lyapunov Functions and Optimization
Further details available from the COCANA Website. 
May 5th
*Saturday, 8:304:00* *Seattle* 
WCOM

Details of the Spring 2018
West Coast Optimization Meeting held at UW Seattle are
here.

Apr. 20th
*Friday* *4:305:30* *SUR 2710* 
Jingxin Guo
M.Sc. project presentation Senior Supervisor: A. Punnen 
The Unrestricted Linear Fractional Assignment Problem
Abstract: The linear fractional assignment problem (LFAP) is a wellstudied combinatorial optimization problem with various applications. It attempts to minimize ratio of two linear functions subject to standard assignment constraints. When the denominator of the objective function is positive, LFAP is solvable in polynomial time. However, when the denominator of the objective function is allowed to take positive and negative values, LFAP is known to be NPhard. In this thesis, we present two 01 programming formulations of LFAP and compare their relative merits using experimental analysis. We also show that LFAP can be solved as a polynomial bounded sequence of constrained assignment problems. Experimental results using this methodology are also given. Finally, some local search heuristics are developed and analyzed their efficiency using systematic experimental analysis. Our algorithms are able to solve reasonably large size problems within acceptable computational time. 
Apr. 10th
*11:30* *SUR 2980* 
Negin Bolkhanian and Matthew Reyers
Simon Fraser University 
Math 402W Operations Research Clinic
project presentation
The Walking School Bus Routing Problem 
Apr. 10th
*10:30* *SUR 2980* 
Alan Bi, Trevor Dallow and Samantha Zimmerman
Simon Fraser University 
Math 402W Operations Research Clinic
project presentation
Scheduling of Nurses at Raven Song Community Health Care Centre 
Apr. 5th
via COCANA (Kelowna) 
Yves Lucet
UBC Okanagan 
On the convexity of piecewisedefined functions
Further details available from the COCANA Website. 
Mar. 15th

Sandy Rutherford
Complex Systems Modelling Group Simon Fraser University 
Control of an HIV Epidemic among Injection Drug Users:
Simulation Modeling on Complex Networks
Abstract: HIV remains a serious public health problem in many marginalized communities. We develop a network model of the HIV epidemic affecting injection drug users and female sex workers in the Downtown Eastside neighborhood of Vancouver, Canada, calibrated using data from public health surveillance and cohort studies. Many HIV positive individuals are unaware of their status and strategies for testing are an important part of HIV response programs. Upon diagnosis, HIV patients enter a continuum of care, involving both engagement and retention in treatment. We explored potential epidemic control strategies through simulation: reduced syringe sharing during injection drug use, reduced time to diagnosis, reduced time to initiation of treatment following diagnosis, and improved retention in treatment. We find that syringe sharing, HIV testing, and retention in treatment significantly impact HIV prevalence. Close connections between syringe sharing and sexual networks deserve attention as important avenues for rapid HIV transmission. 
Mar. 8th
via COCANA (Kelowna) 
Tim Hoheisel
McGill University 
Epiconvergent Smoothing with Applications to ConvexComposite Functions
Further details available from the COCANA Website. 
Mar. 1st
SUR 3040 
Winfried Grassmann
Computer Science University of Saskatchewan 
Discrete Event Systems as Basis of Discretetime Queues, Including Multiserver Queues and Tandem Queues
Abstract: A number of papers have appeared describing how to calculate the distribution of the number of elements in a discretetime GI/G/1 queue in a statistical equilibrium. Essentially, the process is converted to a discretetime Markov chain and solved as such. It turns out that this method also works for discretetime discrete event systems in a statistical equilibrium. They, too, can be converted into discrete time Markov chains, and solved. The problem is that due to the curse of dimensionality, the number of states is huge, and to solve the equilibrium equations, iterative methods should be used, such as GaussSeidel. Still, every effort must be made to reduce the dimensionality of the problem as much as possible. One way to do this is to embed the process at the points in time where events occur. Using this method, we could solve systems of reasonable size on our laptop, including GI/G/c queues and tandem queues. For some models, further reductions in the dimensionality are possible. One example is the applications of the distributional Littleās law to the GI/G/1 queue. Possible extensions of this method are discussed. 
Feb. 22nd
*SUR 3040* 
David Stanford
Statistics and Actuarial Science Western (Ontario) University 
The Affine Accumulating Priority Queue: a model which prioritises based upon acuity and waiting time
Abstract: Previous accumulating priority queues (APQ) in the literature have assumed that all arriving customers accumulate priority credits over time starting from an initial value of 0. The affine APQ model introduces a new element in terms of an initial classdependent credit level, from which the accumulated priority grows linearly over time. In this presentation, we consider a twoclass APQ, for which class1 customers receive a positive initial credit upon arrival. (Without loss of generality the class2 customers continue to have an initial credit of 0.) We assess the impact of the initial priority score upon the waiting time distribution for the lower class of customers, and insights regarding the higher priority class waiting time distribution as well. Numerical examples will be presented to illustrate the trends we observe. This is joint work with Maryam Mojalal, Richard Caron, Peter Taylor and Ilze Ziedins. 
Jan. 25th
via COCANA (Kelowna) *SUR 2746* 
Paulo J. S. Silva
Unicamp 
Using the Spectral Proximal Gradient Method to Decompose a Matrix as the Sum of a Sparse Plus a Lowrank Term
Further details available from the COCANA Website. 
Dec. 11th
*Monday* *9:0010:30* *SUR 2710* 
Bolong He
M.Sc. project presentation Senior Supervisor: T. Stephen 
Analysis of Firefighter Absences and Hiring Schedule Optimization at the Surrey Fire Department
Abstract: We study staffing issues at the Surrey Fire Department with a view to understanding and optimizing the annual hiring cycle for fulltime firefighters. This project begins with a discussion of a previous model used by the Fire Department which predicts absences based on seasonally adjusted historical data and then optimizes the hiring cycle based on a simulation. We extend the analysis of the data to include the age cohort as a variable and compare shortterm and longterm absences. We then use time series to predict future absences and use these predictions along with additional constraints to optimize the hiring schedule. 
Dec. 4th
*Monday* *10:301:00* *SUR 3040* 
Timothy Yusun
Ph.D. thesis defence Senior Supervisor: T. Stephen 
On the Circuit Diameters of Polyhedra
Abstract: We develop a framework to study the circuit diameters of polyhedra. The circuit diameter is a generalization of the combinatorial (edge) diameter, where walks are permitted to enter the interior of the polyhedron as long as steps are parallel to its circuit directions. Because the circuit diameter is dependent on the specific realization of the polyhedron, many of the techniques used in the edge case do not transfer easily. We reformulate circuit analogues of the Hirsch conjecture, the dstep conjecture, and the nonrevisiting conjecture, recovering the edge case equivalences in the circuit case. To do this we adapt the notion of simplicity to work with circuit diameter, and so we define Csimplicity and wedgesimplicity. Then, we prove the circuit 4step conjecture, including for unbounded polyhedra, by showing that the original counterexample U_{4} to the combinatorial analogue satisfies the Hirsch bound in the circuit case, independent of its realization. This was the first known counterexample to Hirsch, and several families of counterexamples are constructed from U_{4}. In particular, the unbounded Hirsch conjecture could still hold in the circuit case. We also use computational methods to study Q_{4}, the bounded counterpart to U_{4}, and give two realizations with different circuit diameters. It remains open whether Q_{4} is circuit Hirschsharp; however, we are able to lower the distance bound for at least one direction between the two far vertices of Q_{4}. Finally, we present some auxiliary results involving representations of polyhedra and circuit calculations. 
Oct. 26th
via COCANA (Kelowna) 
Hamid Afshari
University of Manitoba and UBC Okanagan 
Improving the Resilience of Energy Flow Exchanges in EcoIndustrial Parks: Optimization Under Uncertainty
Further details available from the COCANA Website. 
Sept. 28th
via COCANA (Kelowna) 
Gord Lovegrove
UBC Okanagan 
Models of Bicycle Rider Perceptions Related to Safety and Comfort
Further details available from the COCANA Website. 
Sept. 16th
*Saturday, 8:304:00* *2740* 
WCOM

Details of the Fall 2017
West Coast Optimization Meeting
here.

Sept. 14th
via COCANA (Kelowna) 
Scott Lindstrom
University of Newcastle (Australia) 
DouglasRachford Method for NonConvex Feasibility Problems
Further details available from the COCANA Website. 