17,101 research outputs found
Approximating 1-dimensional TSP Requires Omega(n log n) Comparisons
We give a short proof that any comparison-based n^(1-epsilon)-approximation
algorithm for the 1-dimensional Traveling Salesman Problem (TSP) requires
Omega(n log n) comparisons.Comment: Superseded by "On the complexity of approximating Euclidean traveling
salesman tours and minimum spanning trees", by Das et al; Algorithmica
19:447-460 (1997
Nearly Linear-Work Algorithms for Mixed Packing/Covering and Facility-Location Linear Programs
We describe the first nearly linear-time approximation algorithms for
explicitly given mixed packing/covering linear programs, and for (non-metric)
fractional facility location. We also describe the first parallel algorithms
requiring only near-linear total work and finishing in polylog time. The
algorithms compute -approximate solutions in time (and work)
, where is the number of non-zeros in the constraint
matrix. For facility location, is the number of eligible client/facility
pairs
On-Line File Caching
In the on-line file-caching problem problem, the input is a sequence of
requests for files, given on-line (one at a time). Each file has a non-negative
size and a non-negative retrieval cost. The problem is to decide which files to
keep in a fixed-size cache so as to minimize the sum of the retrieval costs for
files that are not in the cache when requested. The problem arises in web
caching by browsers and by proxies. This paper describes a natural
generalization of LRU called Landlord and gives an analysis showing that it has
an optimal performance guarantee (among deterministic on-line algorithms).
The paper also gives an analysis of the algorithm in a so-called ``loosely''
competitive model, showing that on a ``typical'' cache size, either the
performance guarantee is O(1) or the total retrieval cost is insignificant.Comment: ACM-SIAM Symposium on Discrete Algorithms (1998
A concept for universal pliers
By modification in existing design, pliers can be made to have one pair of handles that will accept number of different jaws. Concept is useful for light to medium duty service. Complete set of jaws may be made to suit specific hobbies or applications
Appropriations Redux: A Critical Look at the Fiscal Year 1988 Continuing Resolution
On January 25, 1988, in his State of the Union Address, President Reagan blasted Congress for the budget process culminating in the Fiscal Year 1988 (FY 88) continuing resolution. 1 Contending that [m]ost of you in this chamber didn\u27t know what was in this [2100-page] catch all bill and [accompanying conference] report, the President boldly proclaimed that he would not sign another one of these. 2 This damning statement, rather than inciting the hostility associated with unfounded accusations, provoked the wild appreciation associated with a minister preaching to the faithful. Indeed, since Congress\u27s passage of the resolution, pledges of support for the President\u27s stand have been made by enough Congressmen and Senators to sustain such a veto. 3 There is good reason to dislike the FY 88 continuing resolution: the bill shattered Congress\u27s reputation as a deliberative body. Fearing the imminent shutdown of the government, 4 Congress adopted internal rules to preclude debate and amendment and effectively to deny access to the final version of the bill. 5 In essence, the resolution appears the secretive work-product of powerful legislators and their aides. This article\u27s concern is the recent proliferation of continuing resolutions and the legal issues associated with that proliferation -- matters that received only scant attention in my earlier piece on limitation riders. 6 In reviewing the causes and contents of last year\u27s continuing resolution, this article will not altogether remove the negative cast put on continuing resolutions. 7 At the same time, ..
Sequential and Parallel Algorithms for Mixed Packing and Covering
Mixed packing and covering problems are problems that can be formulated as
linear programs using only non-negative coefficients. Examples include
multicommodity network flow, the Held-Karp lower bound on TSP, fractional
relaxations of set cover, bin-packing, knapsack, scheduling problems,
minimum-weight triangulation, etc. This paper gives approximation algorithms
for the general class of problems. The sequential algorithm is a simple greedy
algorithm that can be implemented to find an epsilon-approximate solution in
O(epsilon^-2 log m) linear-time iterations. The parallel algorithm does
comparable work but finishes in polylogarithmic time.
The results generalize previous work on pure packing and covering (the
special case when the constraints are all "less-than" or all "greater-than") by
Michael Luby and Noam Nisan (1993) and Naveen Garg and Jochen Konemann (1998)
Discovery of an Attorney’s Work Product in Subsequent Litigation
During the last century, the industrialization of agriculture has led to changes in the landscape and many important habitats have disappeared. Habitat loss and fragmentation and an increased use of agrichemicals have led to biodiversity declines in the agricultural landscape. The negative impacts on pollinators, in particular, must be taken serious because they provide an important ecosystem service when they pollinate crops. Monitoring of pollinators is therefore important to examine the factors that affect pollination. The pan trap method is commonly used in the monitoring of pollinating insects, but few studies have evaluated the effect of trap color on the collection of different groups of pollinators. Pollinators were collected using the pan trap method with blue, yellow and white bowls to examine if there were difference in the attraction to traps of different colors among different groups of pollinators. Lepturine beetles (Lepturinae spp.), bee beetles (Trichius spp.) and the bumblebees (Bombus spp.) preferred the blue traps while rose chafers (Cetoniidae spp.) and hoverflies (Syrphidae spp.) preferred the yellow traps. Hence pan traps of different colors may be specific for different groups of pollinators
A Bound on the Sum of Weighted Pairwise Distances of Points Constrained to Balls
We consider the problem of choosing Euclidean points to maximize the sum of
their weighted pairwise distances, when each point is constrained to a ball
centered at the origin. We derive a dual minimization problem and show strong
duality holds (i.e., the resulting upper bound is tight) when some locally
optimal configuration of points is affinely independent. We sketch a polynomial
time algorithm for finding a near-optimal set of points.Comment: Cornell ORIE Tech Repor
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