The application of superconducting materials is becoming more and more widespread. Traditionally, the discovery of new superconducting materials relies on the experience of experts and a large number of "trial and error" experiments, which not only increases the cost of experiments but also prolongs the period of discovering new superconducting materials. In recent years, machine learning has been increasingly applied to materials science. Based on this, this manuscript proposes the use of XGBoost model to identify superconductors; the first application of deep forest model to predict the critical temperature of superconductors; the first application of deep forest to predict the band gap of materials; and application of a new sub-network model to predict the Fermi energy level of materials. Compared with our known similar literature, all the above algorithms reach state-of-the-art. Finally, this manuscript uses the above models to search the COD public dataset and identify 50 candidate superconducting materials with possible critical temperature greater than 90 K.

As a novel deep learning model, gcForest has been widely used in various applications. However, the current multi-grained scanning of gcForest produces many redundant feature vectors, and this increases the time cost of the model. To screen out redundant feature vectors, we introduce a hashing screening mechanism for multi-grained scanning and propose a model called HW-Forest which adopts two strategies, hashing screening and window screening. HW-Forest employs perceptual hashing algorithm to calculate the similarity between feature vectors in hashing screening strategy, which is used to remove the redundant feature vectors produced by multi-grained scanning and can significantly decrease the time cost and memory consumption. Furthermore, we adopt a self-adaptive instance screening strategy to improve the performance of our approach, called window screening, which can achieve higher accuracy without hyperparameter tuning on different datasets. Our experimental results show that HW-Forest has higher accuracy than other models, and the time cost is also reduced.

In recent years, deep neural networks have achieved excellent performance in many application scenarios such as face recognition and automatic speech recognition (ASR) [21]. However, deep neural networks are difficult to be interpreted. This defect severely restricts the development of deep learning in a few application scenarios, where the model's interpretability is needed. Moreover, the deep neural networks are very data-hungry due to the large complexity of the models, which means that the model's performance can decrease significantly when the size of the training data decreases [12, 22]. In many real tasks, due to the high cost of data collection and labeling, the amount of labeled training data may be insufficient to train a deep neural network. In such a situation, traditional learning methods such as random forest (R.F.) [3], gradient boosting decision tree (GBDT) [15, 5], support-vector machines (SVMs) [7], etc., are still good choices. By realizing that the essence of deep learning lies in the layer-by-layer processing, in-model feature transformation, and sufficient model complexity [33], recently Zhou and Feng [32] proposed the deep forest model and the gcForest algorithm to achieve forest representation learning. It can achieve excellent performance on a broad range of tasks, and can even perform well on small or middle-scale of data. Later on, a more efficient improvement was presented [24], and it shows that forest is able to do auto-encoder which thought to be a specialty of neural networks [13].

Internet companies are facing the need of handling large scale machine learning applications in a daily basis, and distributed system which can handle extra-large scale tasks is needed. Deep forest is a recently proposed deep learning framework which uses tree ensembles as its building blocks and it has achieved highly competitive results on various domains of tasks. However, it has not been tested on extremely large scale tasks. In this work, based on our parameter server system and platform of artificial intelligence, we developed the distributed version of deep forest with an easy-to-use GUI. To the best of our knowledge, this is the first implementation of distributed deep forest. To meet the need of real-world tasks, many improvements are introduced to the original deep forest model. We tested the deep forest model on an extra-large scale task, i.e., automatic detection of cash-out fraud, with more than 100 millions of training samples. Experimental results showed that the deep forest model has the best performance according to the evaluation metrics from different perspectives even with very little effort for parameter tuning. This model can block fraud transactions in a large amount of money \footnote{detail is business confidential} each day. Even compared with the best deployed model, deep forest model can additionally bring into a significant decrease of economic loss.