merge hw1/2 gradient check
merge hw1/2 gradient check

mindis/2015Talk-DeepLearn-CNN,mindis/2015Talk-DeepLearn-CNN,ccwang002/2015Talk-DeepLearn-CNN,ccwang002/2015Talk-DeepLearn-CNN,ccwang002/2015Talk-DeepLearn-CNN,mindis/2015Talk-DeepLearn-CNN