Estimating treatment effects can assist decision-making in various areas, such as commerce and medicine. One application of the treatment effect estimation is to predict the effect of an advertisement on the purchase result of a customer, known as individual treatment effect (ITE). In online websites, the outcome of an individual can be affected by treatments of other individuals, as people often propagate information with their friends. This is referred to as interference. Prior studies have attempted to model interference for accurate ITE estimation under a static network among individuals. However, the network usually changes over time in real-world applications due to complex social activities among individuals. In this case, the outcomes of individuals can be interfered with not only by treatments for current neighbors but also by past information and treatments for past neighbors, which we refer to as dynamic interference . In this work, we model dynamic interference by developing an architecture to aggregate both the past information of individuals and their neighbors. Specifically, our proposed method contains an attention-based historical aggregation, which models interference received by individuals from previous timestamps, and an attention-based neighbor aggregation, which captures interference received by individuals within every timestamp. Since information about individuals changes over time, we propose a parameter evolution trick to adaptively update the parameters of the model, which enables the model to capture the dynamics effectively. In our experiments on multiple datasets with dynamic interference, our method outperforms existing methods for ITE estimation because they cannot capture dynamic interference, which corroborates the importance of dynamic interference modeling.

Smart traffic management is the cornerstone of Intelligent Transport Systems (ITS). To achieve smooth travel in urban road networks, ITS provide software-based traffic management based on traffic forecasts. Recently, spatial-temporal graph neural networks (STGNNs) have achieved significant improvements in traffic forecasting by taking into account spatial and temporal dependencies in traffic data. However, in spite of being an indispensable statistic in traffic management in urban areas, the length of congestion queues has not been a prediction target. In addition, existing methods have not considered the use of multimodal traffic data for forecasting. Moreover, given the significant impact of ITS on the real world, black-box predictions with less explainability are unreliable. In this paper, we propose aQueueing-theory-based Neural Network (QTNet), which combines data-driven STGNN methods with queueing-theory-based domain knowledge of traffic engineering in order to achieve accurate and explainable predictions. In our queue length prediction experiments using a real-world dataset collected in urban areas of Tokyo, QTNet outperformed the baseline methods including the state-of-the-art STGNNs by 12.6% in RMSE and 9.9% MAE, and particularly for severe congestion, by 8.1% and 8.4%.

Estimating individual treatment effects from observational data is a fundamental problem in causal inference. To accurately estimate treatment effects in the spatial domain, we need to address certain aspects such as how to use the spatial coordinates of covariates and treatments and how the covariates and the treatments interact spatially. We introduce a new problem of predicting treatment effects on time series outcomes from spatial graph data with a hierarchical structure. To address this problem, we propose a spatial intervention neural network (SINet) that leverages the hierarchical structure of spatial graphs to learn a rich representation of the covariates and the treatments and exploits this representation to predict a time series of treatment outcome. Using a multi-agent simulator, we synthesized a crowd movement guidance dataset and conduct experiments to estimate the conditional average treatment effect, where we considered the initial locations of the crowds as covariates, route guidance as a treatment, and number of agents reaching a goal at each time stamp as the outcome. We employed state-of-the-art spatio-temporal graph neural networks and neural network-based causal inference methods as baselines, and show that our proposed method outperformed baselines both quantitatively and qualitatively.

Crowdsourcing has been used to collect data at scale in numerous fields. Triplet similarity comparison is a type of crowdsourcing task, in which crowd workers are asked the question “among three given objects, which two are more similar?”, which is relatively easy for humans to answer. However, the comparison can be sometimes based on multiple views, i.e., different independent attributes such as color and shape. Each view may lead to different results for the same three objects. Although an algorithm was proposed in prior work to produce multiview embeddings, it involves at least two problems: (1) the existing algorithm cannot independently predict multiview embeddings for a new sample, and (2) different people may prefer different views. In this study, we propose an end-to-end inductive deep learning framework to solve the multiview representation learning problem. The results show that our proposed method can obtain multiview embeddings of any object, in which each view corresponds to an independent attribute of the object. We collected two datasets from a crowdsourcing platform to experimentally investigate the performance of our proposed approach compared to conventional baseline methods.

Evaluation of intervention in a multi-agent system, e.g., when humans should intervene in autonomous driving systems, is challenging in various engineering and scientific fields. Estimating the individual treatment effect (ITE) using counterfactual long-term prediction is practical to evaluate such interventions. However, most of the conventional frameworks did not consider the time-varying complex structure of multi-agent relationships and covariate counterfactual prediction. Here we propose an interpretable, counterfactual recurrent network in multi-agent systems to estimate the effect of the intervention. Our model leverages graph variational recurrent neural networks and theory-based computation with domain knowledge for the ITE estimation framework based on long-term prediction of multi-agent covariates and outcomes, which can confirm the circumstances under which the intervention is effective. On simulated models of an automated vehicle with time-varying confounders, we show that our methods achieved lower estimation errors in counterfactual covariates.

Trajectory analysis has been a central problem in applications of location tracking systems. Recently, the (discrete) Fréchet distance becomes a popular approach for measuring the similarity of two trajectories because of its high feature extraction capability. Despite its importance, the Fréchet distance has several limitations: (i) sensitive to noise as a trade-off for its high feature extraction capability; and (ii) it cannot be incorporated into machine learning frameworks due to its non-smooth functions. To address these problems, we propose the Fréchet kernel (FRK), which is associated with a smoothed Fréchet distance using a combination of two approximation techniques. FRK can adaptively acquire appropriate extraction capability from trajectories while retaining robustness to noise. Theoretically, we find that FRK has a positive definite property, hence FRK can be incorporated into the kernel method. We also provide an efficient algorithm to calculate FRK. Experimentally, FRK outperforms other methods, including other kernel methods and neural networks, in various noisy real-data classification tasks.

Link prediction is an extensively studied topic and various methods have been proposed to tackle the task in both heuristic and more sophisticated statistical learning approaches. However, most of them focus on the setting of one single graph. Combining information on multiple graphs with similar topological structures can improve the performance and robustness of link prediction; nevertheless, the alignment between nodes of different networks is not always available, or is only partially known. This study considers the link prediction problem on two unaligned networks simultaneously. A new framework is proposed to integrate link prediction using graph embedding and node alignment using optimal transport. The integrated objective is optimized at once via an iterative algorithm. A showcase of the proposed framework using LINE embedding method is discussed with experiments on three real datasets. The results demonstrate that the integrated formulation shows better link prediction performance over single-graph link prediction methods as well as existing methods that do not directly aim at link prediction. The framework is flexible and theoretically able to integrate with different graph embedding methods, which is demonstrated in additional experiments using node2vec.

Massive datasets of spatial trajectories representing the mobility of a diversity of moving objects are ubiquitous in research and industry. Similarity search of a large collection of trajectories is indispensable for turning these datasets into knowledge. Locality sensitive hashing (LSH) is a powerful technique for fast similarity searches. Recent methods employ LSH and attempt to realize an efficient similarity search of trajectories; however, those methods are inefficient in terms of search time and memory when applied to massive datasets. To address this problem, we present the trajectory-indexing succinct trit-array trie (tSTAT), which is a scalable method leveraging LSH for trajectory similarity searches. tSTAT quickly performs the search on a tree data structure called trie. We also present two novel techniques that enable to dramatically enhance the memory efficiency of tSTAT. One is a node reduction technique that substantially omits redundant trie nodes while maintaining the time performance. The other is a space-efficient representation that leverages the idea behind succinct data structures (i.e., a compressed data structure supporting fast data operations). We experimentally test tSTAT on its ability to retrieve similar trajectories for a query from large collections of trajectories and show that tSTAT performs superiorly in comparison to state-of-the-art similarity search methods.

The datafication of spatio-temporal city-wide events is one essential factor for smart management of the city. For this purpose, the combination of real-time event detection on edge sensor nodes mounted public vehicles, and event accumulation on a server is one realistic and efficient solution. We can analyze the accumulated data to understand complex phenomena occurring in entire the city. In this paper, we introduce a novel datafication procedure of city-wide events by sensor mounted garbage trucks and evaluated the preliminary implementation of event detection system on actual vehicle-mounted sensors.

Analysis of spatio-temporal data is a common research topic that requires the interpolations of unknown locations and the predictions of feature observations by utilizing information about where and when the data were observed. One of the most difficult problems is to make predictions of unknown locations. Tensor factorization methods are popular in this field because of their capability of handling multiple types of spatio-temporal data, dealing with missing values, and providing computationally efficient parameter estimation procedures. However, unlike traditional approaches such as spatial autoregressive models, the existing tensor factorization methods have not tried to learn spatial autocorrelations. These methods employ previously inferred spatial dependencies, often resulting in poor performances on the problem of making interpolations and predictions of unknown locations. In this paper, we propose a new tensor factorization method that estimates low-rank latent factors by simultaneously learning the spatial and temporal autocorrelations. We introduce new spatial autoregressive regularizers based on existing spatial autoregressive models and provide an efficient estimation procedure. With experiments on publicly available traffic transporting data, we demonstrate that our proposed method significantly improves the predictive performances in our problems in comparison to the existing state-of-the-art spatio-temporal analysis methods.

Locally Linear Embedding (LLE) is a popular approach to dimensionality reduction as it can effectively represent nonlinear structures of high-dimensional data. For dimensionality reduction, it computes a nearest neighbor graph from a given dataset where edge weights are obtained by applying the Lagrange multiplier method, and it then computes eigenvectors of the LLE kernel where the edge weights are used to obtain the kernel. Although LLE is used in many applications, its computation cost is significantly high. This is because, in obtaining edge weights, its computation cost is cubic in the number of edges to each data point. In addition, the computation cost in obtaining the eigenvectors of the LLE kernel is cubic in the number of data points. Our approach, Ripple, is based on two ideas: (1) it incrementally updates the edge weights by exploiting the Woodbury formula and (2) it efficiently computes eigenvectors of the LLE kernel by exploiting the LU decomposition-based inverse power method. Experiments show that Ripple is significantly faster than the original approach of LLE by guaranteeing the same results of dimensionality reduction.

Non-negative Tensor Factorization (NTF) is a widely used technique for decomposing a non-negative value tensor into sparse and reasonably interpretable factors. However, NTF performs poorly when the tensor is extremely sparse, which is often the case with real-world data and higher-order tensors. In this paper, we propose Non-negative Multiple Tensor Factorization (NMTF), which factorizes the target tensor and auxiliary tensors simultaneously. Auxiliary data tensors compensate for the sparseness of the target data tensor. The factors of the auxiliary tensors also allow us to examine the target data from several different aspects. We experimentally confirm that NMTF performs better than NTF in terms of reconstructing the given data. Furthermore, we demonstrate that the proposed NMTF can successfully extract spatio-temporal patterns of people's daily life such as leisure, drinking, and shopping activity by analyzing several tensors extracted from online review data sets.

The amount and variety of multimedia data such as images, movies and music available on over social networks are increasing rapidly. However, the ability to analyze and exploit these unorganized multimedia data remains inadequate, even with state-of-the-art media processing techniques. Our finding in this paper is that the emerging social curation service is a promising information source for the automatic understanding and mining of images distributed and exchanged via social media. One remarkable virtue of social curation service datasets is that they are weakly supervised: the content in the service is manually collected, selected and maintained by users. This is very different from other social information sources, and we can utilize this characteristics for media content mining without expensive media processing techniques. In this paper we present a machine learning system for predicting view counts of images in social curation data as the first step to automatic image content evaluation. Our experiments confirm that the simple features extracted from a social curation corpus are much superior in terms of count prediction than the gold-standard image features of computer vision research.