Iowa Lottery Action Special Edition, Dec. 3, 2007

Special edition newsletter for Iowa lottery retailers.

Special investigation of the City of Rathbun for the period July 1, 2003 through November 30, 2007

Special investigation of the City of Rathbun for the period July 1, 2003 through November 30, 2007

On certain greedoid polyhedra, partially indexable scheduling problems and extended restless bandit allocation indices

We present a polyhedral framework for establishing general structural properties on optimal solutions of stochastic scheduling problems, where multiple job classes vie for service resources: the existence of an optimal priority policy in a given family, characterized by a greedoid(whose feasible class subsets may receive higher priority), where optimal priorities are determined by class-ranking indices, under restricted linear performance objectives (partial indexability). This framework extends that of Bertsimas and Niño-Mora (1996), which explained the optimality of priority-index policies under all linear objectives (general indexability). We show that, if performance measures satisfy partial conservation laws (with respect to the greedoid), which extend previous generalized conservation laws, then theproblem admits a strong LP relaxation over a so-called extended greedoid polytope, which has strong structural and algorithmic properties. We present an adaptive-greedy algorithm (which extends Klimov's) taking as input the linear objective coefficients, which (1) determines whether the optimal LP solution is achievable by a policy in the given family; and (2) if so, computes a set of class-ranking indices that characterize optimal priority policies in the family. In the special case of project scheduling, we show that, under additional conditions, the optimal indices can be computed separately for each project (index decomposition). We further apply the framework to the important restless bandit model (two-action Markov decision chains), obtaining new index policies, that extend Whittle's (1988), and simple sufficient conditions for their validity. These results highlight the power of polyhedral methods (the so-called achievable region approach) in dynamic and stochastic optimization.

Special investigation of Hardin County Solid Waste Disposal Commission for the period January 1, 2002 through December 31, 2007

Special investigation of Hardin County Solid Waste Disposal Commission for the period January 1, 2002 through December 31, 2007

Special investigation of the City of Postville for the period July 1, 2000 through June 30, 2006

Special investigation of the City of Postville for the period July 1, 2000 through June 30, 2006

Special investigation of the Area XV Regional Planning Commission located in Ottumwa, Iowa for the period July 1, 2000 through June 30, 2006

Special investigation of the Area XV Regional Planning Commission located in Ottumwa, Iowa for the period July 1, 2000 through June 30, 2006

Special investigation of selected accounts at Burlington High School for the period July 1, 2004 through February 16, 2006

Special investigation of selected accounts at Burlington High School for the period July 1, 2004 through February 16, 2006

Special investigation of the City of Mingo for the period September 1, 2002 through June 30, 2006

Special investigation of the City of Mingo for the period September 1, 2002 through June 30, 2006

On the throughput-WIP trade-off in queueing systems, diminishing returns and the threshold property: A linear programming approach

We present a new unifying framework for investigating throughput-WIP(Work-in-Process) optimal control problems in queueing systems,based on reformulating them as linear programming (LP) problems withspecial structure: We show that if a throughput-WIP performance pairin a stochastic system satisfies the Threshold Property we introducein this paper, then we can reformulate the problem of optimizing alinear objective of throughput-WIP performance as a (semi-infinite)LP problem over a polygon with special structure (a thresholdpolygon). The strong structural properties of such polygones explainthe optimality of threshold policies for optimizing linearperformance objectives: their vertices correspond to the performancepairs of threshold policies. We analyze in this framework theversatile input-output queueing intensity control model introduced byChen and Yao (1990), obtaining a variety of new results, including (a)an exact reformulation of the control problem as an LP problem over athreshold polygon; (b) an analytical characterization of the Min WIPfunction (giving the minimum WIP level required to attain a targetthroughput level); (c) an LP Value Decomposition Theorem that relatesthe objective value under an arbitrary policy with that of a giventhreshold policy (thus revealing the LP interpretation of Chen andYao's optimality conditions); (d) diminishing returns and invarianceproperties of throughput-WIP performance, which underlie thresholdoptimality; (e) a unified treatment of the time-discounted andtime-average cases.

Special investigation of the City of Center Point Library for the period January 1, 2006 through December 6, 2007

Special investigation of the City of Center Point Library for the period January 1, 2006 through December 6, 2007

Special investigation of the City of Schleswig for the period January 1, 2003 through January 31, 2007

Special investigation of the City of Schleswig for the period January 1, 2003 through January 31, 2007

Special report on the City of Norwalk for the period July 1, 2006 through April 9, 2008

Special report on the City of Norwalk for the period July 1, 2006 through April 9, 2008

Special report on the Woodbury County Sheriff’s Office for the period December 1, 2004 through December 31, 2007

Special report on the Woodbury County Sheriff’s Office for the period December 1, 2004 through December 31, 2007

Special investigation of the City of Searsboro for the period July 1, 2000 through October 9, 2006

Special investigation of the City of Searsboro for the period July 1, 2000 through October 9, 2006

Special investigation of the City of Grinnell Police Department for the period January 1, 2006 through April 30, 2008

Special investigation of the City of Grinnell Police Department for the period January 1, 2006 through April 30, 2008