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
126
如前所述，“支付金额关于苹果的价格的导数”的值可以通过计算图的
反向传播求出来。先来看一下结果，如图5
-
5 所示，可以通过计算图的反向
传播求导数（关于如何进行反向传播，接下来马上会介绍）。
图5-5 基于反向传播的导数的传递
× ×
100
2.2
200
1.1
220
1
1.1
2
苹果的个数
消费税
如图5
-
5 所示，反向传播使用与正方向相反的箭头（粗线）表示。反向传
播传递“局部导数”，将导数的值写在箭头的下方。在这个例子中，反向传
播从右向左传递导数的值（1
→
1.1
→
2.2）。从这个结果中可知，“支付金额
关于苹果的价格的导数”的值是 2.2。这意味着，如果苹果的价格上涨 1 日元，
最终的支付金额会增加 2.2日元（严格地讲，如果苹果的价格增加某个微小值，
则最终的支付金额将增加那个微小值的2.2 倍 ）。
这里只求了关于苹果的价格的导数，不过“支付金额关于消费税的导
数”“支付金额关于苹果的个数的导数”等也都可以用同样的方式算出来。并
且，计算中途求得的导数的结果（中间传递的导数）可以被共享，从而可以
高效地计算多个导数。综上，计算图的优点是，可以通过正向传播和反向传
播高效地计算各个变量的导数值。
5.2
链式法则
前面介绍的计算图的正向传播将计算结果正向（从左到右）传递，其计
算过程是我们日常接触的计算过程，所以感觉上可能比较自然。而反向传播
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.