July 2018
Intermediate to advanced
310 pages
8h 21m
Chinese
Content preview from 深度学习入门 : 基于Python的理论与实现
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第 5章 误差反向传播法
124
综上，用计算图解题的情况下，需要按如下流程进行。
1. 构建计算图。
2. 在计算图上，从左向右进行计算。
这里的第2 歩“从左向右进行计算”是一种正方向上的传播，简称为正
向传播（
forward propagation
）。正向传播是从计算图出发点到结束点的传播。
既然有正向传播这个名称，当然也可以考虑反向（从图上看的话，就是从右向左）
的传播。实际上，这种传播称为反向传播（
backward propagation
）。反向传
播将在接下来的导数计算中发挥重要作用。
5.1.2
局部计算
计算图的特征是可以通过传递“局部计算”获得最终结果。“局部”这个
词的意思是“与自己相关的某个小范围”。局部计算是指，无论全局发生了什么，
都能只根据与自己相关的信息输出接下来的结果。
我们用一个具体的例子来说明局部计算。比如，在超市买了2 个苹果和
其他很多东西。此时，可以画出如图5
-
4 所示的计算图。
图5-4 买了2 个苹果和其他很多东西的例子
×
+
100
200
2
1.1
苹果的个数
消费税
×
4620
4200
4000
其他很多东西
复杂的计算
…
如图5
-
4 所示，假设（经过复杂的计算）购买的其他很多东西总共花费
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