“…Unsupervised learning, also known as the clustering method, does not need training samples but only interprets the data by exploring the structure and correlation information between the input data, including K-means [16], ISODATA [17], DBSCAN [18], Fuzzy C-Means [19], etc. Supervised learning needs a group of training samples to train the model, which has obtained the optimal model parameters, and then transplants the trained model to the test samples to observe the behaviors of test samples, including sparse/collaborative representation [20], ensemble learning [21], support vector machine [22]. Unlike unsupervised and supervised learning, semisupervised learning introduces some unlabeled samples into the training process for the sake of improving the robustness of method.…”