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
132
现在来看一个加法的反向传播的具体例子。假设有“10
+
5
=
15”这一计
算，反向传播时，从上游会传来值1.3。用计算图表示的话，如图 5
-
11 所示。
图5-11 加法节点的反向传播的具体例子
+
5
10
15
1.3
1.3
1.3
+
因为加法节点的反向传播只是将输入信号输出到下一个节点，所以如图
5
-
11 所示，反向传播将 1.3 向下一个节点传递。
5.3.2
乘法节点的反向传播
接下来，我们看一下乘法节点的反向传播。这里我们考虑z
=
xy。这个
式子的导数用式（5.6）表示。
（5.6）
根据式（5.6），可以像图5
-
12 那样画计算图。
乘法的反向传播会将上游的值乘以正向传播时的输入信号的“翻转值”
后传递给下游。翻转值表示一种翻转关系，如图5
-
12 所示，正向传播时信号
是x 的话，反向传播时则是y；正向传播时信号是 y的话，反向传播时则是x。
现在我们来看一个具体的例子。比如，假设有“10
×
5
=
50”这一计算，
反向传播时，从上游会传来值1.3。用计算图表示的话，如图 5
-
13 所示。
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