Most existing methods for automatic bilingual dictionary induction rely on prior alignments between the source and target languages, such as parallel corpora or seed dictionaries. For many language pairs, such supervised alignments are not readily available. We propose an unsupervised approach for learning a bilingual dictionary for a pair of languages given their independently-learned monolingual word embeddings. The proposed method exploits local and global structures in monolingual vector spaces to align them such that similar words are mapped to each other. We show empirically that the performance of bilingual correspondents that are learned using our proposed unsupervised method is comparable to that of using supervised bilingual correspondents from a seed dictionary.

In this paper we present a framework for spectral clustering based on the following simple scheme: sample a subset of the input points, compute the clusters for the sampled subset using weighted kernel k-means (Dhillon et al. 2004) and use the resulting centers to compute a clustering for the remaining data points. For the case where the points are sampled uniformly at random without replacement, we show that the number of samples required depends mainly on the number of clusters and the diameter of the set of points in the kernel space. Experiments show that the proposed framework outperforms the approaches based on the Nystrom approximation both in terms of accuracy and computation time.

The Nyström method is a matrix approximation technique that has shown great promise in speeding up spectral clustering. However, when the input matrix is sparse, we show that the traditional Nyström method requires a prohibitively large number of samples to obtain a good approximation. We propose a novel sampling approach to select the landmark points used to compute the Nyström approximation. We show that the proposed sampling approach obeys the same error bound as in Bouneffouf and Birol (2015). To control sample complexity, we propose a selective densification step based on breadth-first traversal. We show that the proposed densification does not change the optimal clustering. Results on real world datasets show that by combining the proposed sampling and densification schemes, we can obtain better accuracy compared to other techniques used for the Nyström method while using significantly fewer samples.

As robots continue to create long-term maps, the amount of information that they need to handle increases over time. In terms of place recognition, this implies that the number of images being considered may increase until exceeding the computational resources of the robot. In this paper we consider a scenario where, given multiple independent large maps, possibly from different cities or locations, a robot must effectively and in real time decide whether it can localize itself in one of those known maps. Since the number of images to be handled by such a system is likely to be extremely large, we find that it is beneficial to decompose the set of images into independent groups or environments. This raises a new question: Given a query image, how do we select the best environment? This paper proposes a similarity criterion that can be used to solve this problem. It is based on the observation that, if each environment is described in terms of its co-occurrent features, similarity between environments can be established by comparing their co-occurrence matrices. We show that this leads to a novel place recognition algorithm that divides the collection of images into environments and arranges them in a hierarchy of inverted indices. By selecting first the relevant environment for the operating robot, we can reduce the number of images to perform the actual loop detection, reducing the execution time while preserving the accuracy. The practicality of this approach is shown through experimental results on several large datasets covering a combined distance of more than 750Km.

This paper presents two approaches to combine two popular mapping strategies, namely Particle Filters and Information Filters. The first method describes how the Particle Filter can be incorporated into the Information Filter framework by building local submaps using the Particle Filter and combining them using a Information Filter to obtain a global map. Using the Particle Filter locally reduces the linearization errors and is useful in handling ambiguous data associations, while the Information Filter keeps track of the uncertainty over long periods of time, thereby avoiding FastSLAM's tendency to become overconfident. The second method shows how the Information Filter can be used in the Particle Filter framework as a simple means of remembering the filter's uncertainty. This can then be used to repopulate particles while closing loops. This not only handles non linearities but is also robust for loop closing because, unlike the Particle Filter, the Information Filter does not exhibit forgetfulness of the trajectory's past.

We present a method for finding paths for multiple Unmanned Air Vehicles (UAVs) such that the sum over their lengths is minimum as they cover a 3D terrain (represented as height fields). The paths are constrained to lie beneath an exposure surface to ensure stealth from enemy outposts. The exposure surface is also computed as a height field. The algorithm greedily clusters the terrain such that gain in visibility per distance would be higher for intra-cluster points than points across clusters. Paths generated on clusters formed by such a per distance visibility metric are reduced by more than 25% over other related decoupled methods. The method is extended to cover terrains with partial visibilities. The advantage of the coupled metric extends under constrained visibility also. We again show performance gain by comparing with an existing decoupled algorithm that solves a similar problem of minimum distance terrain coverage with constrained visibility. The paper reveals that decomposing the terrain based on visibility first and then distance is always better than the other way round to cover the terrain in shorter distances.