1, tf.nn.conv2d
參考：http://blog.csdn.net/mao_xiao_feng/article/details/53444333
2, tf.nn.softmax_cross_entropy_with_logits
參考: http://blog.csdn.net/mao_xiao_feng/article/details/53382790
在這里還有對(duì) softmax 的理解/ cross_entropy的理解
3, tf.global_variables()
參考: http://blog.csdn.net/uestc_c2_403/article/details/72356235
