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排序方式: 共有142条查询结果,搜索用时 15 毫秒
41.
Tomasz Schoen 《Archiv der Mathematik》2010,94(3):219-226
We study additive intersective properties of sparse subsets of integers. In particular, we prove that for every set S with counting function o(log n) there exists a set A with lower asymptotic density 1/2 such that A + A is disjoint from S. We also show that this result is best possible. 相似文献
42.
Given a non empty polyhedral set, we consider the problem of finding a vector belonging to it and having the minimum number
of nonzero components, i.e., a feasible vector with minimum zero-norm. This combinatorial optimization problem is NP-Hard
and arises in various fields such as machine learning, pattern recognition, signal processing. One of the contributions of
this paper is to propose two new smooth approximations of the zero-norm function, where the approximating functions are separable
and concave. In this paper we first formally prove the equivalence between the approximating problems and the original nonsmooth
problem. To this aim, we preliminarily state in a general setting theoretical conditions sufficient to guarantee the equivalence
between pairs of problems. Moreover we also define an effective and efficient version of the Frank-Wolfe algorithm for the
minimization of concave separable functions over polyhedral sets in which variables which are null at an iteration are eliminated
for all the following ones, with significant savings in computational time, and we prove the global convergence of the method.
Finally, we report the numerical results on test problems showing both the usefulness of the new concave formulations and
the efficiency in terms of computational time of the implemented minimization algorithm. 相似文献
43.
44.
A. Grosso A. R. M. J. U. Jamali M. Locatelli F. Schoen 《Journal of Global Optimization》2010,47(1):63-81
In this paper we propose a Monotonic Basin Hopping approach and its population-based variant Population Basin Hopping to solve
the problem of packing equal and unequal circles within a circular container with minimum radius. Extensive computational
experiments have been performed both to analyze the problem at hand, and to choose in an appropriate way the parameter values
for the proposed methods. Different improvements with respect to the best results reported in the literature have been detected. 相似文献
45.
The problem of molecular docking is defined as that of finding a minimum energy configuration of a pair of molecular structures (usually consisting of proteins, DNA or RNA fragments). It is often assumed that the two interacting structures can be considered as rigid bodies and that it is of interest to researchers to develop methods which enable to discover the potential binding sites. Many different models have been proposed in the literature for the definition of the potential energy between two molecular structures, most of which contain at least a term (known as Van Der Waals interaction) which accounts for pairwise attraction between atoms, a repulsion term and a term which takes into account electrostatic forces (Coulomb interaction). Some well known models, and in particular those used in rigid docking, are based on the assumption that the only terms which are relevant in the process of docking are pairwise interactions between atoms belonging to the two different parts of the structure. In this paper the problem of finding the lowest energy configuration of a pair of biomolecular structures, considered as rigid bodies, is defined and formulated as a global optimization problem. In terms of dimension of the search space this formulation is not 'high-dimensional', as there are only six degrees of freedom: 3 translation and 3 rotation parameters. However the energy surface of the docking problem is characterized by a huge number of local minima; moreover each function evaluation is quite expensive (interesting structures usually possess a few thousand atoms each). So there is a strong need both of local and of global optimization procedures. In this paper a local optimization technique, based upon standard non linear programming software and a penalized objective function, is introduced and its potential usefulness in the context of global optimization is outlined. 相似文献
46.
47.
A wide class of test functions for global optimization 总被引:1,自引:0,他引:1
Fabio Schoen 《Journal of Global Optimization》1993,3(2):133-137
48.
Black TC Huffman PR Jacobson DL Snow WM Schoen K Arif M Kaiser H Lamoreaux SK Werner SA 《Physical review letters》2003,90(19):192502
We have performed the first high precision measurement of the coherent neutron scattering length of deuterium in a pure sample using neutron interferometry. We find b(nd)=(6.665+/-0.004) fm in agreement with the world average of previous measurements using different techniques, b(nd)=(6.6730+/-0.0045) fm. We compare the new world average for the nd coherent scattering length b(nd)=(6.669+/-0.003) fm to calculations of the doublet and quartet scattering lengths from several modern nucleon-nucleon potential models with three-nucleon force (3NF) additions and show that almost all theories are in serious disagreement with experiment. This comparison is a more stringent test of the models than past comparisons with the less precisely determined doublet scattering length of (2)a(nd)=(0.65+/-0.04) fm. 相似文献
49.
Ground-state NO2 radicals are formed in <5 ps with a quantum yield of ≈ 70% in 264 nm photolysis of low pressure nitromethane, as revealed by laser-induced fluorescence probing. Raman shifted photolyzing pulses indicate the NO2 yield varies little with wavelength, although a small yield of excited state NO*2 produced at 264 nm increases significantly at 238 nm. 相似文献
50.