“…Based on such a principle, multi-task learning methods emerge and are attracting more and more attentions in the fields of machine learning, data mining and pattern recognition. The existing multi-task learning methods can be categorized into three types: (1) Multi-task classification learning [2,[5][6][7][14][15][16]21,22,33,36,43]; (2) Multi-task clustering [3,18,19,23,42,44]; and (3) Multi-task regression learning [8,27,34,37,45]. Although these works have demonstrated the significance of multi-task learning and certain effectiveness in different real-world applications, the current multi-task learning methods still cannot keep up with the real-world requirements, particularly in regression tasks.…”