Online Learning(from Cousera Course of Stanford University)

1. Since online learning algorithms do not save old examples, they can be very efficent in terms of computer memory and disk space.(在线学习是利用实时流数据，因此不需要保存旧的眼里，节省内存和磁盘空间)；

2. One of the advantages of online learning is that if the function we're modeling

 changes over time (such as if we are modeling the probability of users clicking

 on different URLs, and user tastes/preferences are changing over time), the

 online learning algorithm will automatically adapt to these changes. (在线学习的

优势之一就在于模型会实时变化，因为数据是实时变化，在线学习算法也要自动的随

之变化)；

3. Online learning algorithms are usually best suited to problems were we have a

 continuous/non-stop stream of data that we want to learn from.

4.  In the approach to online learning discussed in the lecture video, we

 repeatedly get a single training example, take one step of stochastic gradient

 descent using that example, and then move on to the next example.(一个新案

例，使用随机梯度下降仍然要学习率 alpha)