[ML] logistic gradient accent and Andrew Ng gradient decent

ref:

http://www.csdn123.com/html/topnews201408/66/10366.htm


the gradient fun is l(n)

normally hope probability biggest, so use gradient Accent to find largest theta of l(n)

but

Andrew Ng set J(theta)=-(1/m)l(n), there has a "-", so become find the minimum , so
use gradient decent.