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Parallel machine scheduling problems concern the scheduling of n jobs on m machines to minimize some function of the job completion times. If preemption is not allowed, then most problems are not only NP-hard, but also very hard from a practical point of view. In this paper, we show that strong and fast linear programming lower bounds can be computed for an(More)
Time-indexed formulations for machine scheduling problems have received a great deal of attention; not only do the linear programming relaxations provide strong lower bounds, but they are good guides for approximation algorithms as well. Unfortunately , time-indexed formulations have one major disadvantage: their size. Even for relatively small instances(More)
We report new results for a time-indexed formulation of nonpreemptive single-machine scheduling problems. We give complete characterizations of all facet inducing inequalities with integral coeecients and right-hand side 1 or 2 for the convex hull of the set of feasible partial schedules, i.e., schedules in which not all jobs have to be started.(More)
It is essential for product software companies to decide which requirements should be included in the next release and to make an appropriate time plan of the development project. Compared to the extensive research done on requirement selection, very little research has been performed on time scheduling. In this paper, we introduce two integer linear(More)
OBJECTIVE To compare the risk of developing diabetes mellitus (DM) in the general population between subjects who had a depression and subjects who never had a depression. METHOD Retrospective cohort design. People with depression were diagnosed with a depression between 1975 and 1990; controls never had a depression. Both groups were followed for a(More)
BACKGROUND Depression has been linked to the occurrence of a number of somatic diseases. There are no data for PD. OBJECTIVE To determine if depression is associated with a subsequent risk for PD. METHODS A retrospective cohort study design based in general practice was applied. All subjects diagnosed with depression between 1975 and 1990 were included(More)
This paper investigates two integer linear programming models that integrate requirement scheduling into software release planning. The first model can schedule the development of the requirements for the new release exactly in time so that the project span is minimized and the resource and precedence constraints are satisfied. The second model is for(More)
BACKGROUND Published prevalence studies on multimorbidity present diverse data collection methods, sources of data, targeted age groups, diagnoses considered and study populations, making the comparability of prevalence estimates questionable. The objective of this study was to compare prevalence estimates of multimorbidity derived from two sources and to(More)