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Search Results: 1 - 10 of 39969 matches for " Robert Luo "
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Towards Minimax Online Learning with Unknown Time Horizon
Haipeng Luo,Robert E. Schapire
Computer Science , 2013,
Abstract: We consider online learning when the time horizon is unknown. We apply a minimax analysis, beginning with the fixed horizon case, and then moving on to two unknown-horizon settings, one that assumes the horizon is chosen randomly according to some known distribution, and the other which allows the adversary full control over the horizon. For the random horizon setting with restricted losses, we derive a fully optimal minimax algorithm. And for the adversarial horizon setting, we prove a nontrivial lower bound which shows that the adversary obtains strictly more power than when the horizon is fixed and known. Based on the minimax solution of the random horizon setting, we then propose a new adaptive algorithm which "pretends" that the horizon is drawn from a distribution from a special family, but no matter how the actual horizon is chosen, the worst-case regret is of the optimal rate. Furthermore, our algorithm can be combined and applied in many ways, for instance, to online convex optimization, follow the perturbed leader, exponential weights algorithm and first order bounds. Experiments show that our algorithm outperforms many other existing algorithms in an online linear optimization setting.
Achieving All with No Parameters: Adaptive NormalHedge
Haipeng Luo,Robert E. Schapire
Computer Science , 2015,
Abstract: We study the classic online learning problem of predicting with expert advice, and propose a truly parameter-free and adaptive algorithm that achieves several objectives simultaneously without using any prior information. The main component of this work is an improved version of the NormalHedge.DT algorithm (Luo and Schapire, 2014), called AdaNormalHedge. On one hand, this new algorithm ensures small regret when the competitor has small loss and almost constant regret when the losses are stochastic. On the other hand, the algorithm is able to compete with any convex combination of the experts simultaneously, with a regret in terms of the relative entropy of the prior and the competitor. This resolves an open problem proposed by Chaudhuri et al. (2009) and Chernov and Vovk (2010). Moreover, we extend the results to the sleeping expert setting and provide two applications to illustrate the power of AdaNormalHedge: 1) competing with time-varying unknown competitors and 2) predicting almost as well as the best pruning tree. Our results on these applications significantly improve previous work from different aspects, and a special case of the first application resolves another open problem proposed by Warmuth and Koolen (2014) on whether one can simultaneously achieve optimal shifting regret for both adversarial and stochastic losses.
A Drifting-Games Analysis for Online Learning and Applications to Boosting
Haipeng Luo,Robert E. Schapire
Computer Science , 2014,
Abstract: We provide a general mechanism to design online learning algorithms based on a minimax analysis within a drifting-games framework. Different online learning settings (Hedge, multi-armed bandit problems and online convex optimization) are studied by converting into various kinds of drifting games. The original minimax analysis for drifting games is then used and generalized by applying a series of relaxations, starting from choosing a convex surrogate of the 0-1 loss function. With different choices of surrogates, we not only recover existing algorithms, but also propose new algorithms that are totally parameter-free and enjoy other useful properties. Moreover, our drifting-games framework naturally allows us to study high probability bounds without resorting to any concentration results, and also a generalized notion of regret that measures how good the algorithm is compared to all but the top small fraction of candidates. Finally, we translate our new Hedge algorithm into a new adaptive boosting algorithm that is computationally faster as shown in experiments, since it ignores a large number of examples on each round.
Impact of miRNA Sequence on miRNA Expression and Correlation between miRNA Expression and Cell Cycle Regulation in Breast Cancer Cells
Zijun Luo, Yi Zhao, Robert Azencott
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0095205
Abstract: The miRNAs regulate cell functions by inhibiting expression of proteins. Research on miRNAs had usually focused on identifying targets by base pairing between miRNAs and their targets. Instead of identifying targets, this paper proposed an innovative approach, namely impact significance analysis, to study the correlation between mature sequence, expression across patient samples or time and global function on cell cycle signaling of miRNAs. With three distinct types of data: The Cancer Genome Atlas miRNA expression data for 354 human breast cancer specimens, microarray of 266 miRNAs in mouse Embryonic Stem cells (ESCs), and Reverse Phase Protein Array (RPPA) transfected by 776 miRNAs in MDA-MB-231 cell line, we linked the expression and function of miRNAs by their mature sequence and discovered systematically that the similarity of miRNA expression enhances the similarity of miRNA function, which indicates the miRNA expression can be used as a supplementary factor to predict miRNA function. The results also show that both seed region and 3' portion are associated with miRNA expression levels across human breast cancer specimens and in ESCs; miRNAs with similar seed tend to have similar 3' portion. And we discussed that the impact of 3' portion, including nucleotides , is not significant for miRNA function. These results provide novel insights to understand the correlation between miRNA sequence, expression and function. They can be applied to improve the prediction algorithm and the impact significance analysis can also be implemented to similar analysis for other small RNAs such as siRNAs.
Racial and Ethnic Variations in Preventive Dental Care Utilization among Middle-Aged and Older Americans, 1999–2008
Bei Wu,Huabin Luo,Robert Furter
Frontiers in Public Health , 2013, DOI: 10.3389/fpubh.2013.00065
Abstract: Objective: This study examined recent trends of preventive dental care utilization among Americans aged 50 and above, focusing on variations across racial and ethnic groups including Whites, Blacks, Hispanics, American Indians/Alaska Natives, and Asians.
Quantitative Determination of Metallic Iron Content in Steel-Making Slag  [PDF]
Zhiyong Xu, Jim Hwang, Robert Greenlund, Xiaodi Huang, Jinjing Luo, Steve Anschuetz
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2003, DOI: 10.4236/jmmce.2003.21006
Abstract: A quantitative analytical method for metallic iron was developed for wastes from iron and steel mills. These wastes consist of slags, dusts and sludges, mill scales, spent pickle liquor, and other iron-bearing materials. Accurate determination of metallic iron in these wastes will provide the vital information for the recycling or reuse of these wastes. The new procedure for the determination of metallic iron (Fe0) was developed and various factors that could affect the test result were determined. Pure metallic iron powders were mixed with pure iron oxides with various ratios and then were tested using this method. Testing results had excellent agreement with actual concentration. Samples from several sites have been tested.
Gene Order Phylogeny of the Genus Prochlorococcus
Haiwei Luo, Jian Shi, William Arndt, Jijun Tang, Robert Friedman
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003837
Abstract: Background Using gene order as a phylogenetic character has the potential to resolve previously unresolved species relationships. This character was used to resolve the evolutionary history within the genus Prochlorococcus, a group of marine cyanobacteria. Methodology/Principal Findings Orthologous gene sets and their genomic positions were identified from 12 species of Prochlorococcus and 1 outgroup species of Synechococcus. From this data, inversion and breakpoint distance-based phylogenetic trees were computed by GRAPPA and FastME. Statistical support of the resulting topology was obtained by application of a 50% jackknife resampling technique. The result was consistent and congruent with nucleotide sequence-based and gene-content based trees. Also, a previously unresolved clade was resolved, that of MIT9211 and SS120. Conclusions/Significance This is the first study to use gene order data to resolve a bacterial phylogeny at the genus level. It suggests that the technique is useful in resolving the Tree of Life.
Zr$_5$Sb$_3$$_-$$_x$Ru$_x$, a new superconductor in the W$_5$Si$_3$ structure type
Weiwei Xie,Huixia Luo,Brendan F. Phelan,Robert J. Cava
Physics , 2015,
Abstract: We report that at low Ru contents, up to x = 0.2, the Zr$_5$Sb$_3$$_-$$_x$Ru$_x$ solid solution forms in the hexagonal Mn$_5$Si$_3$ structure type of the host (x = 0), but that at higher Ru contents (x = 0.4 - 0.6) the solid solution transforms into the tetragonal W$_5$Si$_3$ structure type. We find that tetragonal Zr$_5$Sb$_2$$_.$$_4$Ru$_0$$_.$$_6$ is superconducting at 5 K, significantly higher than the transition temperature of hexagonal Zr$_5$Sb$_3$ (x = 0), which has a T$_c$ of 2.3 K. In support of a hypothesis that certain structure types are favorable for superconductivity, we describe how the W$_5$Si$_3$ and Tl$_5$Te$_3$ structure types, both of which support superconductivity, are derived from the parent Al$_2$Cu type structure, in which superconductors are also found. Electronic structure calculations show that in Zr$_1$$_0$Sb$_5$Ru, a model for the new superconducting compound, the Fermi level is located on a peak in the electronic density of states.
Fast Convergence of Regularized Learning in Games
Vasilis Syrgkanis,Alekh Agarwal,Haipeng Luo,Robert E. Schapire
Computer Science , 2015,
Abstract: We show that natural classes of regularized learning algorithms with a form of recency bias achieve faster convergence rates to approximate efficiency and to coarse correlated equilibria in multiplayer normal form games. When each player in a game uses an algorithm from our class, their individual regret decays at $O(T^{-3/4})$, while the sum of utilities converges to an approximate optimum at $O(T^{-1})$--an improvement upon the worst case $O(T^{-1/2})$ rates. We show a black-box reduction for any algorithm in the class to achieve $\tilde{O}(T^{-1/2})$ rates against an adversary, while maintaining the faster rates against algorithms in the class. Our results extend those of [Rakhlin and Shridharan 2013] and [Daskalakis et al. 2014], who only analyzed two-player zero-sum games for specific algorithms.
The joint influence of marital status, interpregnancy interval, and neighborhood on small for gestational age birth: a retrospective cohort study
Nathalie Auger, Mark Daniel, Robert W Platt, Zhong-Cheng Luo, Yuquan Wu, Robert Choinière
BMC Pregnancy and Childbirth , 2008, DOI: 10.1186/1471-2393-8-7
Abstract: We analyzed a cohort of 98,330 live births in Montréal, Canada from 1997–2001 to assess IPI and marital status in relation to small for gestational age (SGA) birth. Births were categorized as subsequent-born with short (<12 months), intermediate (12–35 months), or long (36+ months) IPI, or as firstborn. The data had a 2-level hierarchical structure, with births nested in 49 neighborhoods. We used multilevel logistic regression to obtain adjusted effect estimates.Marital status modified the association between IPI and SGA birth. Being unmarried relative to married was associated with SGA birth for all IPI categories, particularly for subsequent births with short (odds ratio [OR] 1.60, 95% confidence interval [CI] 1.31–1.95) and intermediate (OR 1.48, 95% CI 1.26–1.74) IPIs. Subsequent births had a lower likelihood of SGA birth than firstborns. Intermediate IPIs were more protective for married (OR 0.50, 95% CI 0.47–0.54) than unmarried mothers (OR 0.65, 95% CI 0.56–0.76).Being unmarried increases the likelihood of SGA birth as the IPI shortens, and the protective effect of intermediate IPIs is reduced in unmarried mothers. Marital status should be considered in recommending particular IPIs as an intervention to improve birth outcomes.The relationship between interpregnancy interval (IPI) and perinatal health is receiving increasing attention. A recent meta-analysis concluded that the IPI, defined as time between the last delivery and conception of the current pregnancy, can be associated with adverse birth outcomes when the IPI is either too short or too long [1]. The promotion of appropriate pregnancy spacing has been recommended to achieve better birth outcomes [2].Although research on the IPI has been performed in many countries, relatively few studies have been conducted in developed nations characterized by low rates of adverse birth outcomes and comprehensive health insurance such as Canada [1]. Furthermore, studies on the IPI have not accounted for residential
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