clustering

Power system stability, control, and design studies are time-consuming due to the formation of large size and heavy interconnection networks. Reduced ordered dynamic equivalent methods are thus so desirable for performing these studies. Simple equivalents are obtained by converting large and complex networks into smaller networks. One of the approaches to the problem of model reduction is to find coherency-based generator grouping and aggregation. In this method, first, based on network characteristics, each group of coherent generators is replaced with a dynamic equivalent, and then the dynamic equivalent of the generators is used in the studies of power networks. In this regard, in this article, using graph theory and clustering quality index, a novel method for finding coherent generators in a power network is presented. The proposed method is simple and the network admittance matrix is the only information required by this approach. The IEEE 39-bus network is used to show the effectiveness of the proposed approach. The comparison of the results with other research shows that the proposed method identifies the coherent generators with an acceptable approximation.

Clustering is an operation in which a set of data samples is categorized according to the degree of similarity. Examples of clustering data are numerical or a mixture of numerical and non-numerical (nominal) data. Finding similarities and measuring distances is one of the challenges of mixed data clustering. In the related works, to detect the degree of similarity and obtain the distance value, only the parameter of the distance value was considered and the cluster was selected based on its value. Clustering in this way, especially for mixed data, has not had very accurate results. In this paper, we have tried to pay attention to the parameter "number of similar features" in calculating the degree of similarity and determining the distance. In assigning each sample to a cluster in cases where the distances are equal or close, the number of common features of the samples will determine the appropriate cluster. That is, we will pay attention to the "number of similar features" in addition to the distance to select the cluster. This idea believes that in cases where the distance of the cluster centers is close to the data object, it is better to choose the cluster center that has more features similar to the data object. Logically and also according to the proposed algorithm, the amount of similarity should be in a larger number of features, not just a few limited features but with high similarity. The parameter of the "number of similar features" has a specific definition and is obtained with a suitable threshold. If the distance value of two features is less than the threshold, those two features are considered as similar features. To calculate the distance in the algorithm, the normalized numerical difference for numerical properties and the Hamming distance for non-numerical properties are used. Determining the initial cluster centers, like many methods, is done randomly, and in subsequent iterations of the algorithm, more appropriate samples are selected as the cluster centers. The algorithm is compared with 5 other algorithms in 5 datasets. In examining the results, three criteria of Accuracy, RI and F-Measure have been used. According to the test results, in the mixed and integer datasets, the algorithm performs at least two percent better than the two algorithms and one percent better than the other algorithm. In another data set, the proposed algorithm had results equal to or close to one percent better accuracy than the superior algorithm. In the last data set, the proposed algorithm was ranked second among 5 algorithms. In general, the proposed algorithm won the top rank in most of the results, and in the rest of the cases, it won the second rank out of the five tested algorithms.

This paper presents a new method for using data collected from the agent's random movement in the environment for the initial adjustment of parameters of a controller with a fuzzy reinforcement learning structure. Slow learning speed and high failure rates during training are two major challenges in such structures. The initial parameterization of the fuzzy system can be a suitable solution to address these challenges. In this paper, the method of discrete value iteration is extended to continuous without relying on derivative based methods to initialize the parameters of the fuzzy system. First, random interaction with the environment is used to collect relevant data. Since the state space is continuous, the data is appropriately clustered and each cluster is considered as a state. Then, by generalizing the standard value iteration method to the continuous, the transition probability matrix and the immediate reward expectation matrix are calculated. Using the results of this stage, the initial parameterization of the fuzzy reinforcement learning structure is performed. Subsequently, these parameters are fine-tuned using reinforcement learning. The proposed method is called "Value Iteration based Fuzzy Reinforcement Learning" and is used in the problem of target following robots. The experimental results indicate a significant improvement in the performance of the proposed method in the problem of target following robots.

Face recognition poses challenges in accuracy, memory efficiency, and computational complexity. This study proposes a two-stage, three-module approach: Subnetwork modules, Cluster-Finder unit, and Final-Decision module. Unlike random distribution methods, our approach employs clustering for distribution. Each subnetwork, a supervised deep neural network, is trained with cluster-specific data. The Cluster-Finder unit compares test data similarity with each subnetwork’s representative. The Final-Decision module selects the best class. Results indicate superior accuracy, recall, and F1 score compared to competitive methods. The approach is faster and more accurate than non-distribution methods, with comparable speed and higher accuracy than random distribution methods. Experiments on VGGFace2, MS-Celeb-1M, and Glint360K datasets confirm both superior performance and scalability. The proposed method, using KMeans for distribution, outperforms Softmax Dissection and Dynamic Active Class Selection. It simplifies training without additional manipulations, offering efficiency over methodologies like Softmax Dissection and ArcFace parallelization. In conclusion, this study focuses on pre-processing and post-processing without added training complexity. A divide-and-conquer approach addresses accuracy and efficiency challenges. In this study, various sources leading to errors in face recognition systems have been examined. These sources include: imprecise features, overfitting, challenging classes, distribution issues, and decision-making complexities. Various classification scenarios are explored, including non-distributed and models with random and intelligent distributions. Inaccurate features uniformly impact all scenarios, with overfitting posing the greatest challenge in non-distributed scenarios. Challenging classes are better distinguished in intelligent distribution scenarios. Inappropriate distribution has less impact in intelligent scenarios, and decision-making challenges exist in both distributions

Nowadays, high-entropy alloys (HEAs) are a popular domain for researchers which is improved performance by using machine learning (ML). HEAs are formed at least five main elements with close or equal size which is depend on their size and type of elements to extend physical and mechanical features. The ML approach has many applications in various fields. Social network analysis (SNA) is one of the ML tools that is used graph theory. Each graph consists of a number of nodes and edges that each node has its own descriptors. The studies done so far has not used the high-entropy alloys network dataset based on the similarity of content and structural features of each compound. In this paper, a new method is proposed that generalized SNA tools to metallurgical and materials engineering. The proposed method is investigated the HEAs descriptors, in which HEAs descriptors similarity are calculated and the HEAs interaction network is created. The groups have been extracted by Louvain algorithm which each group called cluster. The clusters have alloys with similar properties. The experimental results shown high quality clusters that will be effective in predicting the compounds functionality and discovering new compounds and descriptors. The modularity criterion indicates the quality of the clusters, is about 0.713.

Recommender systems are systems that, over time, learn what product(s) or item(s) each person or customer is (are) likely to like and recommend it (them) to him/her. These systems often operate based on similar behaviors from other (possibly similar) people. Finding similar people is generally a highly time-consuming process due to the large number of users and inaccurate due to the lack of information. For this reason, some methods have resorted to increasing speed. On the other hand, some other methods have added additional information so that they can increase the accuracy of finding similar or neighboring users. Some others have resorted to hybrid methods. Recently, by the use of basic clustering methods, which is based on finding the most similar neighbors with the help of users’ clustering, as well as by using basic content analysis methods and sometimes adding ontology to these methods, researchers have been able to take the advantage of these methods in order to solve some of the above challenges acceptably. In the proposed hybrid recommender system, we have used a two-stage system in which, in the first stage, two models of predictions are made, then in the second stage, by a combining component, the results of the first two parts are combined and the obtained results are given to us as the final results of the system. In the first part, a system based on imputation of missing values fills in the blanks in the scoring matrix. For this end, among the methods of the missing data imputation, we designed a method that was compatible with filling the data set in very sparse conditions, and then generalized it to our own method. In this regard, we have proposed a method based on the grey distance clustering. In the second part, which itself is a hybrid ontology-based recommender system, we first extract the information of each item with the help of a web crawler, then based on a basic article, we produce our own limited ontology, and after that we apply our proposed method. Then, with the help of a proposed method, we improve the ontology structure, thus increasing the accuracy of measuring semantic similarity between the items and users in later stages, and significantly improving the effectiveness of the created recommendations. It should be noted that this ontology is not comprehensive. Finally, we measure the similarity of item-items, user-users, and user-items using an innovative basic ontology similarity measurement method. By the use of this similarity matrix, we cluster users and items, and then store similar users and items as a new feature in the user/item profile for each user/item. This will help us speed up the process of looking for similar users and similar items in the future. In fact, based on this feature, we have increased the speed of the whole work. Since we have set our goal to build a system that makes a balance between the two criteria of accuracy and speed, we use these two criteria to evaluate the proposed system using a real data set. The results of comparing our proposed method with some up-to-date similar methods presented in this field (using the same data set) implies that our method is slower than fast methods, although it is more accurate than them. These results also suggest that the proposed method is faster than accurate methods and its quality is more competitive or even better than them.

The increase of cameras nowadays, and the power of the media in people's lives lead to a staggering amount of video data. It is certain that a method to process this large volume of videos quickly and optimally becomes especially important. With the help of video summarization, this task is achieved and the film is summarized into a series of short but meaningful frames or clips. This study tried to cluster the data by an algorithm (K-Medoids) and then with the help of a convolutional graph attention network, temporal and graph separation is done, then in the next step with the connection rejection method, noises and duplicates are removed, and finally summarization is done by merging the results obtained from two different graphical and temporal steps. The results were analyzed qualitatively and quantitatively on three datasets SumMe, TVSum, and OpenCv. In the qualitative method, an average of 88% accuracy rate in summarization and 31% error rate was achieved, which is one of the highest accuracy rates compared to other methods. In quantitative evaluation, the proposed method has a higher efficiency than the existing methods.

Nowadays, we are witnessing financial markets becoming more competitive, and banks are facing many challenges to attract more deposits from depositors and increase their fee income. Meanwhile, many banks use performance-based incentive plans to encourage their employees to achieve their short-term goals. In the meantime, fairness in the payment of bonuses is one of the important challenges of banks, because not paying attention to this issue can become a factor that destroys the motivation among employees and prevents the bank from achieving its short-term and mid-term goals. This article is trying to tackle the problem of optimizing the coefficients of branch performance evaluation indicators based on their business environment in one of the state banks of Iran. In this article, a two-objective genetic algorithm is proposed to solve the problem. This article is comprised of four main sections. The first section is dedicated to the problem definition which is what is our meaning of optimizing the importance coefficients of branches based on the business environment. The second section is about our proposed solution for the defined problem. In the third section, we are comparing the performance of the proposed two-objective genetic algorithm on the defined problem with the performance of four well-known multi-objective algorithms including NSGAII, SPEAII, PESAII, and MOEA/D. And finally, the set of ZDT problems which is a standard set of multi-objective problems is taken into account for evaluating the general performance of the proposed algorithm comparing four well-known multi-objective algorithms. Our proposed solution for solving the problem of optimizing branch performance coefficients includes two main steps. First, identifying the business environment of the branches and second, optimizing the coefficients with the proposed two-objective genetic algorithm. In the first step, the k-means clustering algorithm is applied to cluster branches with similar business environments. In the second step, to optimize the coefficients, it is necessary to specify the fitness functions. The defined problem is a two-objective problem, the first objective is to minimize the deviation of the real performance of the branches from the expected performance of them, and the second objective is to minimize the deviation of the coefficients from the coefficients determined by the experts. To solve this two-objective problem, a two-objective genetic algorithm is proposed. In this article, two approaches are adopted to compare the proposed solution performance. In the first stage, the results of applying the proposed two-objective genetic algorithm have been compared with the results of applying four well-known multi-objective genetic algorithms on the problem of optimizing the coefficients. The results of this comparison show that the proposed algorithm has outperformed the other compared methods based on the S indicator and run time, and it is also ranked second after the NSGAII algorithm in terms of the HV indicator. Finally, for evaluating the performance of the proposed algorithm with other well-known methods, the set of ZDT problems including ZDT1, ZDT2, ZDT3, ZDT4, and ZDT6 has also been taken into consideration. At this stage, the performance of the proposed algorithm has been compared with the four mentioned algorithms based on four key indicators, including GD, S, H, and run time. The results show, the proposed algorithm has outperformed significantly in terms of run time in all five ZDT problems. In terms of GD indicator, the performance of our proposed algorithm is located in the first or second rank among all considered algorithms. In addition, in terms of S and H indicators in many cases, the proposed algorithm outperformed the other well-known algorithms.

Calculation and applying trust among users has become popular in designing recommender systems in recent years. However, most of the trust-based recommender systems use only one factor for estimating the value of trust. In this paper, a multi-factor approach for estimating trust among users of recommender systems is introduced. In the proposed scheme, first, users of the system are clustered based on their similarities in demographics information and history of ratings. To predict the rating of the active user into a specific item, the value of trust between him and the other users in his cluster is calculated considering the factors i.e. time, location, and context of their rating. To this end, we propose an algorithm based on beta distribution. A novel tree-based measure for computing the semantic similarity between the contexts is utilized. Finally, the rating of the active user is predicted using weighted averaging where trust values are considered as weights. The proposed scheme was performed on three datasets, and the obtained results indicated that it outperforms existing methods in terms of accuracy and other efficiency metrics.