Knowledge graph (KG) embedding is a fundamental problem in mining relational patterns. It aims to encode the entities and relations in KG into low dimensional vector space that can be used for subsequent algorithms. Lots of KG embedding models have been proposed to learn the interactions between entities and relations, which contain meaningful semantic information. However, structural information, which encodes local topology among entities, is also important to KG. In this work, we propose S2E to distill structural information and combine it with semantic information for different KGs as a neural architecture search (NAS) problem. First, we analyze the difficulty of using a unified model to solve the distillation problem. Based on it, we define the path distiller to recurrently combine structural and semantic information along relational paths, which are sampled to preserve both local topologies and semantics. Then, inspired by the recent success of NAS, we design a recurrent network-based search space for specific KG tasks and propose a natural gradient (NG) based search algorithm to update architectures. Experimental results demonstrate that the searched models by our proposed S2E outperform human-designed ones, and the NG based search algorithm is efficient compared with other NAS methods. Besides, our work is the first NAS method for RNN that can search architectures with better performance than human-designed models.

A well-constructed classification model highly depends on input feature subsets from a dataset, which may contain redundant, irrelevant, or noisy features. This challenge can be worse while dealing with medical datasets. The main aim of feature selection as a pre-processing task is to eliminate these features and select the most effective ones. In the literature, metaheuristic algorithms show a successful performance to find optimal feature subsets. In this paper, two binary metaheuristic algorithms named S-shaped binary Sine Cosine Algorithm (SBSCA) and V-shaped binary Sine Cosine Algorithm (VBSCA) are proposed for feature selection from the medical data. In these algorithms, the search space remains continuous, while a binary position vector is generated by two transfer functions S-shaped and V-shaped for each solution. The proposed algorithms are compared with four latest binary optimization algorithms over five medical datasets from the UCI repository. The experimental results confirm that using both bSCA variants enhance the accuracy of classification on these medical datasets compared to four other algorithms.

We frame OPE as a covariate-shift problem and leverage modern robust regression tools. Ours is a general approach that can be used to augment any existing OPE method that utilizes the direct method. When augmenting doubly robust methods, we call the resulting method triply robust, since we add robustness to the direct method used in doubly robust. We prove upper bounds on the resulting bias and variance, as well as derive novel minimax bounds based on robust minimax analysis for covariate shift. Our robust regression method is compatible with deep learning, and is thus applicable to complex OPE settings that require powerful function approximators. Finally, we demonstrate superior empirical performance across the standard OPE benchmarks, especially in the case where the logging policy is unknown and must be estimated from data. 1 Introduction Contextual bandits is the online learning setting where a policy repeatedly observes a context, takes an action, and then observes a reward only for the chosen action [Langford and Zhang, 2007].

Social activities play an important role in people's daily life since they interact. For recommendations based on social activities, it is vital to have not only the activity information but also individuals' social relations. Thanks to the geo-social networks and widespread use of location-aware mobile devices, massive geo-social data is now readily available for exploitation by the recommendation system. In this paper, a novel group recommendation method, called attentive geo-social group recommendation, is proposed to recommend the target user with both activity locations and a group of users that may join the activities. We present an attention mechanism to model the influence of the target user $u_T$ in candidate user groups that satisfy the social constraints. It helps to retrieve the optimal user group and activity topic candidates, as well as explains the group decision-making process. Once the user group and topics are retrieved, a novel efficient spatial query algorithm SPA-DF is employed to determine the activity location under the constraints of the given user group and activity topic candidates. The proposed method is evaluated in real-world datasets and the experimental results show that the proposed model significantly outperforms baseline methods.

In this work, we introduce Graph Pointer Networks (GPNs) trained using reinforcement learning (RL) for tackling the traveling salesman problem (TSP). GPNs build upon Pointer Networks by introducing a graph embedding layer on the input, which captures relationships between nodes. Furthermore, to approximate solutions to constrained combinatorial optimization problems such as the TSP with time windows, we train hierarchical GPNs (HG-PNs) using RL, which learns a hierarchical policy to find an optimal city permutation under constraints. Each layer of the hierarchy is designed with a separate reward function, resulting in stable training. Our results demonstrate that GPNs trained on small-scale TSP50/100 problems generalize well to larger-scale TSP500/1000 problems, with shorter tour lengths and faster computational times. We verify that for constrained TSP problems such as the TSP with time windows, the feasible solutions found via hierarchical RL training outperform previous baselines. In the spirit of reproducible research we make our data, models, and code publicly available.

In this paper, we propose a new wrapper approach for semi-supervised feature selection. A common strategy in semi-supervised learning is to augment the training set by pseudo-labeled unlabeled examples. However, the pseudo-labeling procedure is prone to error and has a high risk of disrupting the learning algorithm with additional noisy labeled training data. To overcome this, we propose to model explicitly the mislabeling error during the learning phase with the overall aim of selecting the most relevant feature characteristics. We derive a $\mathcal{C}$-bound for Bayes classifiers trained over partially labeled training sets by taking into account the mislabeling errors. The risk bound is then considered as an objective function that is minimized over the space of possible feature subsets using a genetic algorithm. In order to produce both sparse and accurate solution, we propose a modification of a genetic algorithm with the crossover based on feature weights and recursive elimination of irrelevant features. Empirical results on different data sets show the effectiveness of our framework compared to several state-of-the-art semi-supervised feature selection approaches.

Integrating ML models in software is of growing interest. Building accurate models requires right choice of hyperparameters for training procedures (learners), when the training dataset is given. AutoML tools provide APIs to automate the choice, which usually involve many trials of different hyperparameters for a given training dataset. Since training and evaluation of complex models can be time and resource consuming, existing AutoML solutions require long time or large resource to produce accurate models for large scale training data. That prevents AutoML to be embedded in a software which needs to repeatedly tune hyperparameters and produce models to be consumed by other components, such as large-scale data systems. We present a fast and lightweight hyperparameter optimization method FLO and use it to build an efficient AutoML solution. Our method optimizes for minimal evaluation cost instead of number of iterations to find accurate models. Our main idea is to leverage a holistic consideration of the relations among model complexity, evaluation cost and accuracy. FLO has a strong anytime performance and significantly outperforms Bayesian Optimization and random search for hyperparameter tuning on a large open source AutoML Benchmark. Our AutoML solution also outperforms top-ranked AutoML libraries in a majority of the tasks on this benchmark.

Maximising the detection of intrusions is a fundamental and often critical aim of perimeter surveillance. Commonly, this requires a decision-maker to optimally allocate multiple searchers to segments of the perimeter. We consider a scenario where the decision-maker may sequentially update the searchers' allocation, learning from the observed data to improve decisions over time. In this work we propose a formal model and solution methods for this sequential perimeter surveillance problem. Our model is a combinatorial multi-armed bandit (CMAB) with Poisson rewards and a novel filtered feedback mechanism - arising from the failure to detect certain intrusions. Our solution method is an upper confidence bound approach and we derive upper and lower bounds on its expected performance. We prove that the gap between these bounds is of constant order, and demonstrate empirically that our approach is more reliable in simulated problems than competing algorithms.

We study online optimization in a setting where an online learner seeks to optimize a per-round hitting cost, which may be non-convex, while incurring a movement cost when changing actions between rounds. We ask: \textit{under what general conditions is it possible for an online learner to leverage predictions of future cost functions in order to achieve near-optimal costs?} Prior work has provided near-optimal online algorithms for specific combinations of assumptions about hitting and switching costs, but no general results are known. In this work, we give two general sufficient conditions that specify a relationship between the hitting and movement costs which guarantees that a new algorithm, Synchronized Fixed Horizon Control (SFHC), provides a $1+O(1/w)$ competitive ratio, where $w$ is the number of predictions available to the learner. Our conditions do not require the cost functions to be convex, and we also derive competitive ratio results for non-convex hitting and movement costs. Our results provide the first constant, dimension-free competitive ratio for online non-convex optimization with movement costs. Further, we give an example of a natural instance, Convex Body Chasing (CBC), where the sufficient conditions are not satisfied and we can prove that no online algorithm can have a competitive ratio that converges to 1.

Experimentation has become an increasingly prevalent tool for guiding policy choices, firm decisions, and product innovation. A common hurdle in designing experiments is the lack of statistical power. In this paper, we study optimal multi-period experimental design under the constraint that the treatment cannot be easily removed once implemented; for example, a government or firm might implement treatment in different geographies at different times, where the treatment cannot be easily removed due to practical constraints. The design problem is to select which units to treat at which time, intending to test hypotheses about the effect of the treatment. When the potential outcome is a linear function of a unit effect, a time effect, and observed discrete covariates, we provide an analytically feasible solution to the design problem where the variance of the estimator for the treatment effect is at most 1+O(1/N^2) times the variance of the optimal design, where N is the number of units. This solution assigns units in a staggered treatment adoption pattern, where the proportion treated is a linear function of time. In the general setting where outcomes depend on latent covariates, we show that historical data can be utilized in the optimal design. We propose a data-driven local search algorithm with the minimax decision criterion to assign units to treatment times. We demonstrate that our approach improves upon benchmark experimental designs through synthetic experiments on real-world data sets from several domains, including healthcare, finance, and retail. Finally, we consider the case where the treatment effect changes with the time of treatment, showing that the optimal design treats a smaller fraction of units at the beginning and a greater share at the end.