Machine Learning definition
1） Arthur Samuel(1959 跳棋游戏)给出的定义：
Field of study that gives computers the ability to learn without being explicitly programmed.(在没有明确设置的情况下，使计算机具有学习能力的研究领域
2）Tom M.Mitchell 给出的定义
A computer program is said to learn from experience E with respect to some task T and some performance measure P, if its performance on T, as mearsured by P, improves with experience E.