Sanghamitra Bandyopadhyay

Monalisa Pal, Sanghamitra Bandyopadhyay

Multi-modal multi-objective optimization problems (MMMOPs) have multiple subsets within the Pareto-optimal Set, each independently mapping to the same Pareto-Front. Prevalent multi-objective evolutionary algorithms are not purely designed to search for multiple solution subsets, whereas, algorithms designed for MMMOPs demonstrate degraded performance in the objective space. This motivates the design of better algorithms for addressing MMMOPs. The present work identifies the crowding illusion problem originating from using crowding distance globally over the entire decision space. Subsequently, an evolutionary framework, called graph Laplacian based Optimization using Reference vector assisted Decomposition (LORD), is proposed, which uses decomposition in both objective and decision space for dealing with MMMOPs. Its filtering step is further extended to present LORD-II algorithm, which demonstrates its dynamics on multi-modal many-objective problems. The efficacies of the frameworks are established by comparing their performance on test instances from the CEC 2019 multi-modal multi-objective test suite and polygon problems with the state-of-the-art algorithms for MMMOPs and other multi- and many-objective evolutionary algorithms. The manuscript is concluded by mentioning the limitations of the proposed frameworks and future directions to design still better algorithms for MMMOPs. The source code is available at https://worksupplements.droppages.com/lord.

Angana Chakraborty, Sanghamitra Bandyopadhyay

Locality Sensitive Hashing (LSH) based algorithms have already shown their promise in finding approximate nearest neighbors in high dimen- sional data space. However, there are certain scenarios, as in sequential data, where the proximity of a pair of points cannot be captured without considering their surroundings or context. In videos, as for example, a particular frame is meaningful only when it is seen in the context of its preceding and following frames. LSH has no mechanism to handle the con- texts of the data points. In this article, a novel scheme of Context based Locality Sensitive Hashing (conLSH) has been introduced, in which points are hashed together not only based on their closeness, but also because of similar context. The contribution made in this article is three fold. First, conLSH is integrated with a recently proposed fast optimal sequence alignment algorithm (FOGSAA) using a layered approach. The resultant method is applied to video retrieval for extracting similar sequences. The pro- posed algorithm yields more than 80% accuracy on an average in different datasets. It has been found to save 36.3% of the total time, consumed by the exhaustive search. conLSH reduces the search space to approximately 42% of the entire dataset, when compared with an exhaustive search by the aforementioned FOGSAA, Bag of Words method and the standard LSH implementations. Secondly, the effectiveness of conLSH is demon- strated in action recognition of the video clips, which yields an average gain of 12.83% in terms of classification accuracy over the state of the art methods using STIP descriptors. The last but of great significance is that this article provides a way of automatically annotating long and composite real life videos. The source code of conLSH is made available at http://www.isical.ac.in/~bioinfo_miu/conLSH/conLSH.html