ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 02 Oct 2022 09:35:43 GMT2022-10-02T09:35:43Z5051- Controlled dual perturbations for central path trajectories in geometric programminghttps://scholarbank.nus.edu.sg/handle/10635/44944Title: Controlled dual perturbations for central path trajectories in geometric programming
Authors: Zhu, J.; Kortanek, K.O.; Huang, S.
Abstract: A dynamic perturbation algorithm is developed building on the work of Fang, Peterson and Rajasekera, who introduced simple lower bounds as perturbations in an equivalent dual pair to the posynomial geometric programming primal and dual programs. In their approach, a duality gap tolerance is pre-specified, and then the perturbations are determined from additional information, such as a current feasible point and a bound for the optimal program value. Our approach updates the perturbation vector in at most O(In ε{lunate}) outer loop iterations, while requiring no more than a 50% reduction in the current duality gap in each inner loop iteration. One of the advantages of our approach is that the perturbation bound tends to stay away from zero in a way that results in more stable computations. © 1994.
Sat, 01 Jan 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/449441994-01-01T00:00:00Z
- Note on the problem of scheduling a flexible manufacturing system for just-in-time customershttps://scholarbank.nus.edu.sg/handle/10635/44900Title: Note on the problem of scheduling a flexible manufacturing system for just-in-time customers
Authors: Co, H.C.; Zhu, J.
Abstract: In supplying just-in-time customers, one common industry practice is for the vendor to set up a warehouse near the point of demand. We assume that the plant is a flexible manufacturing system (FMS) where the changeover times between parts of the same family are negligible, but not between parts of different families. Thus the FMS must be configured to produce one family of parts at a time. For each part type, we assume that the vendor makes deliveries to the warehouse at fixed intervals. We examined two related issues: the run length for each part family and the number of deliveries to the warehouse in each cycle. We first showed that it is not necessary for the vendor to produce for each delivery, nor is it desirable to complete the entire production lot before delivery. We then investigated the FMS loading problem for two or more part-families. We developed the expressions for the optimal run length and delivery frequency, (1) when loading the part types sequentially and (2) when loading the part types simultaneously. The resulting models can be shown to be consistent with the classical EOQ model.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/449001995-01-01T00:00:00Z
- Cyclic and constant-proportion input-control strategies for dedicated flexible manufacturing system operationshttps://scholarbank.nus.edu.sg/handle/10635/45004Title: Cyclic and constant-proportion input-control strategies for dedicated flexible manufacturing system operations
Authors: Co, H.; Li, H.; Zhu, J.
Abstract: This paper investigates two input-control strategies for flexible manufacturing systems (FMS). Under cyclic control, the FMS is dedicated to processing one part type at a time, in cyclic order. This strategy limits the variety of parts loaded to the machines at any time to one, and hence simplifies the flow pattern of jobs in the FMS. Another input-control strategy is to maintain a constant proportion of all part types in the family. This strategy leads to production smoothing, i.e., producing the same production mix for each item each day. Intuitively, this control strategy maximizes the flexibility of the machines and minimizes work-in-process. We evaluate the two input-control strategies from the production-inventory-control viewpoint applicable to the FMS operations. © 1995.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/450041995-01-01T00:00:00Z
- Ranking the efficiency performance within a set of decision making units by data envelopment analysishttps://scholarbank.nus.edu.sg/handle/10635/140065Title: Ranking the efficiency performance within a set of decision making units by data envelopment analysis
Authors: Li, Hong-Yu; Zhao, Hongxin; Zhu, Jishan
Fri, 01 Mar 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1400651996-03-01T00:00:00Z
- On controlling the parameter in the logarithmic barrier term for convex programming problemshttps://scholarbank.nus.edu.sg/handle/10635/113908Title: On controlling the parameter in the logarithmic barrier term for convex programming problems
Authors: Kortanek, K.O.; Zhu, J.
Abstract: We present a log-barrier based algorithm for linearly constrained convex differentiable programming problems in nonnegative variables, but where the objective function may not be differentiable at points having a zero coordinate. We use an approximate centering condition as a basis for decreasing the positive parameter of the log-barrier term and show that the total number of iterations to achieve an ε-tolerance optimal solution is O(|log(ε)|)×(number of inner-loop iterations). When applied to the n-variable dual geometric programming problem, this bound becomes O(n2U/ε), where U is an upper bound on the maximum magnitude of the iterates generated during the computation. © 1995 Plenum Publishing Corporation.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1139081995-01-01T00:00:00Z