【知识点】
Random Trees classifier、Boosting classifier, or MLP, or Knearest, or Nbayes, or Support Vector Machines

【数据集】letter-recognition.data，20000*17，前16000行用于训练，后4000行测试。
第1列为label，后16列为特征值（整数，被归一化到0~15范围，主要是统计矩和边缘计数），含义如下：
1. x-box horizontal position of box
2. y-box vertical position of box
3. width width of box
4. high height of box
5. onpix total # on pixels
6. x-bar mean x of on pixels in box
7. y-bar mean y of on pixels in box
8. x2bar mean x variance
9. y2bar mean y variance
10. xybar mean x y correlation
11. x2ybr mean of x * x * y
12. xy2br mean of x * y * y
13. x-ege mean edge count left to right
14. xegvy correlation of x-ege with y
15. y-ege mean edge count bottom to top
16. yegvx correlation of y-ege with x