排序方式: 共有88条查询结果,搜索用时 125 毫秒
41.
We provide the first interesting explicit lower bounds on efficient approximability for two closely related optimization problems
in graphs, MINIMUM EDGE DOMINATING SET and MINIMUM MAXIMAL MATCHING. We show that it is NP-hard to approximate the solution of both problems to within any constant factor smaller than
. The result extends with negligible loss to bounded degree graphs and to everywhere dense graphs.
An extended abstract of this paper was accepted at the 14th Annual International Symposium on Algorithms and Computation,
ISAAC 2003. 相似文献
42.
This paper considers a variation of the classical single machine scheduling problem with tool changes. In the variation, two sets of jobs, namely special jobs and normal jobs, are considered. By special jobs, we mean that each special job must be processed within the first prefixed time units of a tool life. To solve the scheduling problem with small size and moderate size, we propose two mathematical programming models. To solve the scheduling problem with large size, we propose three sets of algorithms and focus on the performance of six algorithms based on the studies of a new bin packing problem. Worst-case analysis is conducted. Numerical experiment shows that each of the six algorithms can solve instances with up to 5000 jobs in about 0.5 s with an average relative error less than 4%. 相似文献
43.
M.N. Goria 《Australian & New Zealand Journal of Statistics》1992,34(1):55-64
We show that, within the family of power transformations of a Chisquare variable, the square and fourth roots minimize Pearson's index of kurtosis. Two new transtormations of the fourth root, a symmetrized-truncated version and its linear combination with the square root are also studied. The first transformation shows a considerable improvement over the fourth root while the second one turns out to be even more accurate than Hilferty-Wilson's cube root transformation. 相似文献
44.
陈历敏 《湛江师范学院学报》2002,23(3):1-3
该文讨论一类数学期望算子的一致逼近问题,借助于文献[1]的渐近估计式.给出了这类算子一致逼近下的正定理. 相似文献
45.
The problem of partitioning a partially ordered set into a minimum number of chains is a well-known problem. In this paper
we study a generalization of this problem, where we not only assume that the chains have bounded size, but also that a weight
w
i
is given for each element i in the partial order such that w
i
≤w
j
if i
≺
j. The problem is then to partition the partial order into a minimum-weight set of chains of bounded size, where the weight
of a chain equals the weight of the heaviest element in the chain. We prove that this problem is
-hard, and we propose and analyze lower bounds for this problem. Based on these lower bounds, we exhibit a 2-approximation
algorithm, and show that it is tight. We report computational results for a number of real-world and randomly generated problem
instances. 相似文献
46.
When ties and incomplete preference lists are permitted in the Stable Marriage and Hospitals/Residents problems, stable matchings
can have different sizes. The problem of finding a maximum cardinality stable matching in this context is known to be NP-hard,
even under very severe restrictions on the number, size and position of ties. In this paper, we describe polynomial-time 5/3-approximation
algorithms for variants of these problems in which ties are on one side only and at the end of the preference lists. The particular
variant is motivated by important applications in large scale centralised matching schemes.
A preliminary version of this paper appeared in the Proceedings of COCOON 2007, LNCS, vol. 4598, pp. 548–558.
This work was supported by EPSRC grant EP/E011993/1. 相似文献
47.
《统计学通讯:模拟与计算》2013,42(4):1249-1250
Abstract In this article several formulae for the approximation of the critical values for tests on the actual values of the process capability indices CPL, CPU, and Cpk are provided. These formulae are based on different approximations of the percentiles of the noncentral t distribution and their performance is evaluated by comparing the values assessed through them from the exact critical values, for several significance levels, test values, and sample sizes. As supported by the obtained results, some of the presented techniques constitute valuable tools in situations where the exact critical values of the tests are not available, since one may approximate them readily and rather accurately through them. 相似文献
48.
Cossette et al. (2010, 2011) gave a novel collective risk model where the total numbers of claims satisfy the first-order integer-valued autoregressive process. For a risk model, it is interesting to investigate the upper bound of ruin probability. However, the loss increments of the above model are dependent; it is difficult to derive the upper bound of ruin probability. In this article, we propose an approximation model with stationary independent increments. The upper bound of ruin probability and the adjustment coefficient are derived. The approximation model is illustrated via four simulated examples. Results show that the gap of the approximation model and dependent model can be ignored by adjusting values of parameters. 相似文献
49.
Daniel Ackerberg John Geweke Jinyong Hahn 《Econometrica : journal of the Econometric Society》2009,77(6):2009-2017
We show by counterexample that Proposition 2 in Fernández‐Villaverde, Rubio‐Ramírez, and Santos (Econometrica (2006), 74, 93–119) is false. We also show that even if their Proposition 2 were corrected, it would be irrelevant for parameter estimates. As a more constructive contribution, we consider the effects of approximation error on parameter estimation, and conclude that second order approximation errors in the policy function have at most second order effects on parameter estimates. 相似文献
50.
Michael H. Neumann 《Statistics》2013,47(1):33-63
Theory in time series analysis is often developed under the assumption of finite-dimensional models for the data generating process. Whereas corresponding estimators such as those of a conditional mean function are reasonable even if the true dependence mechanism is more complex, it is usually necessary to capture the whole dependence structure asymptotically for the bootstrap to be valid. In contrast, we show that certain simplified bootstrap schemes which imitate only some aspects of the time series are consistent for quantities arising in nonparametric statistics. To this end, we generalize the well-known "whitening by windowing" principle to joint distributions of nonparametric estimators of the autoregression function. Consequently, we obtain that model-based nonparametric bootstrap schemes remain valid for supremum-type functionals as long as they mimic those finite-dimensional joint distributions consistently which determine the quantity of interest. As an application, we show that simple regression-type bootstrap schemes can be applied for the determination of critical values for nonparametric tests of parametric or semiparametric hypotheses on the autoregression function in the context of a general process. 相似文献