吴恩达深度学习课程一：神经网络和深度学习 第三周：浅层神经网络（二）

经过第二周的基础补充，本周内容的理解难度可以说有了很大的降低，主要是从逻辑回归扩展到浅层神经网络，讲解相关内容，我们按部就班梳理课程内容即可，当然，依旧会尽可能地创造一个较为丝滑的理解过程。
我们继续上一篇的内容，来展开一下激活函数对浅层神经网络拟合效果的影响，并完成浅层神经网络的反向传播部分，这样，我们就大致了解了浅层神经网络相比逻辑回归，是如何提高算法性能的。

1. 浅层神经网络里的激活函数

1.1 隐藏层激活函数的作用

在逻辑回归中，我们知道，最后使用sigmoid激活函数是为了让加权和映射为概率从而实现分类效果。
而现在，如果我们仍要进行二分类，而浅层神经网络输出层的sigmoid函数已经实现了分类效果，那隐藏层再使用激活函数的作用是什么？
我们看一看如果不设隐藏层神经元的激活函数，正向传播的输出是什么形式：

https://www.bilibili.com/read/cv43483089
https://www.bilibili.com/read/cv43483089/
https://www.bilibili.com/opus/1127334584896192544
https://www.bilibili.com/read/cv43483088
https://www.bilibili.com/read/cv43483088/
https://www.bilibili.com/opus/1127334563403530246
https://www.bilibili.com/read/cv43483086
https://www.bilibili.com/read/cv43483086/
https://www.bilibili.com/opus/1127334537654698019
https://www.bilibili.com/read/cv43483085
https://www.bilibili.com/read/cv43483085/
https://www.bilibili.com/opus/1127334511826173977
https://www.bilibili.com/read/cv43483084
https://www.bilibili.com/read/cv43483084/
https://www.bilibili.com/opus/1127334490377551895
https://www.bilibili.com/read/cv43483083
https://www.bilibili.com/read/cv43483083/
https://www.bilibili.com/opus/1127334464584679431
https://www.bilibili.com/read/cv43483081
https://www.bilibili.com/read/cv43483081/
https://www.bilibili.com/opus/1127334438811729923
https://www.bilibili.com/read/cv43483079
https://www.bilibili.com/read/cv43483079/
https://www.bilibili.com/opus/1127334413098549271
https://www.bilibili.com/read/cv43483078
https://www.bilibili.com/read/cv43483078/
https://www.bilibili.com/opus/1127334391605886981
https://www.bilibili.com/read/cv43483076
https://www.bilibili.com/read/cv43483076/
https://www.bilibili.com/opus/1127334365853909001
https://www.bilibili.com/read/cv43483073
https://www.bilibili.com/read/cv43483073/
https://www.bilibili.com/opus/1127334340043210805
https://www.bilibili.com/read/cv43483070
https://www.bilibili.com/read/cv43483070/
https://www.bilibili.com/opus/1127334318611365891
https://www.bilibili.com/read/cv43483068
https://www.bilibili.com/read/cv43483068/
https://www.bilibili.com/opus/1127334292794376243
https://www.bilibili.com/read/cv43483067
https://www.bilibili.com/read/cv43483067/
https://www.bilibili.com/opus/1127334267049738278
https://www.bilibili.com/read/cv43483066
https://www.bilibili.com/read/cv43483066/
https://www.bilibili.com/opus/1127334245545541641
https://www.bilibili.com/read/cv43483065
https://www.bilibili.com/read/cv43483065/
https://www.bilibili.com/opus/1127334219775737880
https://www.bilibili.com/read/cv43483063
https://www.bilibili.com/read/cv43483063/
https://www.bilibili.com/opus/1127334194043682849
https://www.bilibili.com/read/cv43483062
https://www.bilibili.com/read/cv43483062/
https://www.bilibili.com/opus/1127334172543680515
https://www.bilibili.com/read/cv43483060
https://www.bilibili.com/read/cv43483060/
https://www.bilibili.com/opus/1127334052313956361
https://www.bilibili.com/read/cv43483058
https://www.bilibili.com/read/cv43483058/
https://www.bilibili.com/opus/1127334026533666822
https://www.bilibili.com/read/cv43483057
https://www.bilibili.com/read/cv43483057/
https://www.bilibili.com/opus/1127334005064073238
https://www.bilibili.com/read/cv43483054
https://www.bilibili.com/read/cv43483054/
https://www.bilibili.com/opus/1127333979261763586
https://www.bilibili.com/read/cv43483053
https://www.bilibili.com/read/cv43483053/
https://www.bilibili.com/opus/1127333953500348467
https://www.bilibili.com/read/cv43483050
https://www.bilibili.com/read/cv43483050/
https://www.bilibili.com/opus/1127333932064309257
https://www.bilibili.com/read/cv43483047
https://www.bilibili.com/read/cv43483047/
https://www.bilibili.com/opus/1127333906261999619
https://www.bilibili.com/read/cv43483046
https://www.bilibili.com/read/cv43483046/
https://www.bilibili.com/opus/1127333880495341574
https://www.bilibili.com/read/cv43483045
https://www.bilibili.com/read/cv43483045/
https://www.bilibili.com/opus/1127333859044622342
https://www.bilibili.com/read/cv43483044
https://www.bilibili.com/read/cv43483044/
https://www.bilibili.com/opus/1127333833224486930
https://www.bilibili.com/read/cv43483043
https://www.bilibili.com/read/cv43483043/
https://www.bilibili.com/opus/1127333807451537458
https://www.bilibili.com/read/cv43483041
https://www.bilibili.com/read/cv43483041/
https://www.bilibili.com/opus/1127333785985089536
https://www.bilibili.com/read/cv43483040
https://www.bilibili.com/read/cv43483040/
https://www.bilibili.com/opus/1127333760203751443
https://www.bilibili.com/read/cv43483039
https://www.bilibili.com/read/cv43483039/
https://www.bilibili.com/opus/1127333734455967801
https://www.bilibili.com/read/cv43483038
https://www.bilibili.com/read/cv43483038/
https://www.bilibili.com/opus/1127333712957014040
https://www.bilibili.com/read/cv43483036
https://www.bilibili.com/read/cv43483036/
https://www.bilibili.com/opus/1127333687228104741
https://www.bilibili.com/read/cv43483033
https://www.bilibili.com/read/cv43483033/
https://www.bilibili.com/opus/1127333661463543830
https://www.bilibili.com/read/cv43483031
https://www.bilibili.com/read/cv43483031/
https://www.bilibili.com/opus/1127333639997095937
https://www.bilibili.com/read/cv43483029
https://www.bilibili.com/read/cv43483029/
https://www.bilibili.com/opus/1127333614219952178
https://www.bilibili.com/read/cv43483028
https://www.bilibili.com/read/cv43483028/
https://www.bilibili.com/opus/1127333588449099810
https://www.bilibili.com/read/cv43483022
https://www.bilibili.com/read/cv43483022/
https://www.bilibili.com/opus/1127333343619186691
https://www.bilibili.com/read/cv43483021
https://www.bilibili.com/read/cv43483021/
https://www.bilibili.com/opus/1127333317859868710
https://www.bilibili.com/read/cv43483020
https://www.bilibili.com/read/cv43483020/
https://www.bilibili.com/opus/1127333292094259235
https://www.bilibili.com/read/cv43483019
https://www.bilibili.com/read/cv43483019/
https://www.bilibili.com/opus/1127333270626762785
https://www.bilibili.com/read/cv43483018
https://www.bilibili.com/read/cv43483018/
https://www.bilibili.com/opus/1127333244837036048
https://www.bilibili.com/read/cv43483015
https://www.bilibili.com/read/cv43483015/
https://www.bilibili.com/opus/1127333219076669443
https://www.bilibili.com/read/cv43483014
https://www.bilibili.com/read/cv43483014/
https://www.bilibili.com/opus/1127333197611270148
https://www.bilibili.com/read/cv43483011
https://www.bilibili.com/read/cv43483011/
https://www.bilibili.com/opus/1127333171803717666
https://www.bilibili.com/read/cv43483009
https://www.bilibili.com/read/cv43483009/
https://www.bilibili.com/opus/1127333146026573846
https://www.bilibili.com/read/cv43483007
https://www.bilibili.com/read/cv43483007/
https://www.bilibili.com/opus/1127333124603117572
https://www.bilibili.com/read/cv43483006
https://www.bilibili.com/read/cv43483006/
https://www.bilibili.com/opus/1127333098838556695
https://www.bilibili.com/read/cv43483003
https://www.bilibili.com/read/cv43483003/
https://www.bilibili.com/opus/1127333073017372712
https://www.bilibili.com/read/cv43483001
https://www.bilibili.com/read/cv43483001/
https://www.bilibili.com/opus/1127333051587624984
https://www.bilibili.com/read/cv43482998
https://www.bilibili.com/read/cv43482998/
https://www.bilibili.com/opus/1127333025817821223
https://www.bilibili.com/read/cv43482995
https://www.bilibili.com/read/cv43482995/
https://www.bilibili.com/opus/1127332995746758661
https://www.bilibili.com/read/cv43482991
https://www.bilibili.com/read/cv43482991/
https://www.bilibili.com/opus/1127332969979052040
https://www.bilibili.com/read/cv43482990
https://www.bilibili.com/read/cv43482990/
https://www.bilibili.com/opus/1127332944200859653
https://www.bilibili.com/read/cv43482987
https://www.bilibili.com/read/cv43482987/
https://www.bilibili.com/opus/1127332922741751848
https://www.bilibili.com/read/cv43482986
https://www.bilibili.com/read/cv43482986/
https://www.bilibili.com/opus/1127332896967753752
https://www.bilibili.com/read/cv43482985
https://www.bilibili.com/read/cv43482985/
https://www.bilibili.com/opus/1127332871183269921
https://www.bilibili.com/read/cv43482983
https://www.bilibili.com/read/cv43482983/
https://www.bilibili.com/opus/1127332849730453542
https://www.bilibili.com/read/cv43482981
https://www.bilibili.com/read/cv43482981/
https://www.bilibili.com/opus/1127332823939678215
https://www.bilibili.com/read/cv43482979
https://www.bilibili.com/read/cv43482979/
https://www.bilibili.com/opus/1127332798173020199
https://www.bilibili.com/read/cv43482978
https://www.bilibili.com/read/cv43482978/
https://www.bilibili.com/opus/1127332776710766601
https://www.bilibili.com/read/cv43482976
https://www.bilibili.com/read/cv43482976/
https://www.bilibili.com/opus/1127332750938865672
https://www.bilibili.com/read/cv43482974
https://www.bilibili.com/read/cv43482974/
https://www.bilibili.com/opus/1127332725164867605
https://www.bilibili.com/read/cv43482973
https://www.bilibili.com/read/cv43482973/
https://www.bilibili.com/opus/1127332703690031111
https://www.bilibili.com/read/cv43482971
https://www.bilibili.com/read/cv43482971/
https://www.bilibili.com/opus/1127332677911838742
https://www.bilibili.com/read/cv43482970
https://www.bilibili.com/read/cv43482970/
https://www.bilibili.com/opus/1127332652144132145
https://www.bilibili.com/read/cv43482968
https://www.bilibili.com/read/cv43482968/
https://www.bilibili.com/opus/1127332630666149896
https://www.bilibili.com/read/cv43482967
https://www.bilibili.com/read/cv43482967/
https://www.bilibili.com/opus/1127332604857548823
https://www.bilibili.com/read/cv43482965
https://www.bilibili.com/read/cv43482965/
https://www.bilibili.com/opus/1127332579127590936
https://www.bilibili.com/read/cv43482963
https://www.bilibili.com/read/cv43482963/
https://www.bilibili.com/opus/1127332557623394327
https://www.bilibili.com/read/cv43482962
https://www.bilibili.com/read/cv43482962/
https://www.bilibili.com/opus/1127332531849396248
https://www.bilibili.com/read/cv43482959
https://www.bilibili.com/read/cv43482959/
https://www.bilibili.com/opus/1127332506092175397
https://www.bilibili.com/read/cv43482958
https://www.bilibili.com/read/cv43482958/
https://www.bilibili.com/opus/1127332484646699016
https://www.bilibili.com/read/cv43482957
https://www.bilibili.com/read/cv43482957/
https://www.bilibili.com/opus/1127332458881089538
https://www.bilibili.com/read/cv43482956
https://www.bilibili.com/read/cv43482956/
https://www.bilibili.com/opus/1127332433062002688
https://www.bilibili.com/read/cv43482953
https://www.bilibili.com/read/cv43482953/
https://www.bilibili.com/opus/1127332411643789314
https://www.bilibili.com/read/cv43482952
https://www.bilibili.com/read/cv43482952/
https://www.bilibili.com/opus/1127332385814216728
https://www.bilibili.com/read/cv43482950
https://www.bilibili.com/read/cv43482950/
https://www.bilibili.com/opus/1127332360066433045
https://www.bilibili.com/read/cv43482948
https://www.bilibili.com/read/cv43482948/
https://www.bilibili.com/opus/1127332334285094928
https://www.bilibili.com/read/cv43482947
https://www.bilibili.com/read/cv43482947/
https://www.bilibili.com/opus/1127332312854298631
https://www.bilibili.com/read/cv43482944
https://www.bilibili.com/read/cv43482944/
https://www.bilibili.com/opus/1127332287057231895
https://www.bilibili.com/read/cv43482941
https://www.bilibili.com/read/cv43482941/
https://www.bilibili.com/opus/1127332261314691076
https://www.bilibili.com/read/cv43482939
https://www.bilibili.com/read/cv43482939/
https://www.bilibili.com/opus/1127332239823077395
https://www.bilibili.com/read/cv43482938
https://www.bilibili.com/read/cv43482938/
https://www.bilibili.com/opus/1127332214073196581
https://www.bilibili.com/read/cv43482937
https://www.bilibili.com/read/cv43482937/
https://www.bilibili.com/opus/1127332192570048546
https://www.bilibili.com/read/cv43482935
https://www.bilibili.com/read/cv43482935/
https://www.bilibili.com/opus/1127332166789758981
https://www.bilibili.com/read/cv43482934
https://www.bilibili.com/read/cv43482934/
https://www.bilibili.com/opus/1127332141033586705
https://www.bilibili.com/read/cv43482931
https://www.bilibili.com/read/cv43482931/
https://www.bilibili.com/opus/1127332119555604482
https://www.bilibili.com/read/cv43482930
https://www.bilibili.com/read/cv43482930/
https://www.bilibili.com/opus/1127332093816209412
https://www.bilibili.com/read/cv43482929
https://www.bilibili.com/read/cv43482929/
https://www.bilibili.com/opus/1127332067984539687
https://www.bilibili.com/read/cv43482928
https://www.bilibili.com/read/cv43482928/
https://www.bilibili.com/opus/1127332046520188933
https://www.bilibili.com/read/cv43482926
https://www.bilibili.com/read/cv43482926/
https://www.bilibili.com/opus/1127332020783939605
https://www.bilibili.com/read/cv43482924
https://www.bilibili.com/read/cv43482924/
https://www.bilibili.com/opus/1127331995034058768
https://www.bilibili.com/read/cv43482921
https://www.bilibili.com/read/cv43482921/
https://www.bilibili.com/opus/1127331973526716440
https://www.bilibili.com/read/cv43482920
https://www.bilibili.com/read/cv43482920/
https://www.bilibili.com/opus/1127331947772641287
https://www.bilibili.com/read/cv43482919
https://www.bilibili.com/read/cv43482919/
https://www.bilibili.com/opus/1127331922016469013
https://www.bilibili.com/read/cv43482918
https://www.bilibili.com/read/cv43482918/
https://www.bilibili.com/opus/1127331900524855329
https://www.bilibili.com/read/cv43482917
https://www.bilibili.com/read/cv43482917/
https://www.bilibili.com/opus/1127331874721497127
https://www.bilibili.com/read/cv43482915
https://www.bilibili.com/read/cv43482915/
https://www.bilibili.com/opus/1127331848996782151
https://www.bilibili.com/read/cv43482913
https://www.bilibili.com/read/cv43482913/
https://www.bilibili.com/opus/1127331823214395413
https://www.bilibili.com/read/cv43482912
https://www.bilibili.com/read/cv43482912/
https://www.bilibili.com/opus/1127331801746898944
https://www.bilibili.com/read/cv43482911
https://www.bilibili.com/read/cv43482911/
https://www.bilibili.com/opus/1127331775985483779
https://www.bilibili.com/read/cv43482910
https://www.bilibili.com/read/cv43482910/
https://www.bilibili.com/opus/1127331750167445507
https://www.bilibili.com/read/cv43482909
https://www.bilibili.com/read/cv43482909/
https://www.bilibili.com/opus/1127331724434341896
https://www.bilibili.com/read/cv43482908
https://www.bilibili.com/read/cv43482908/
https://www.bilibili.com/opus/1127331702922805251
https://www.bilibili.com/read/cv43482907
https://www.bilibili.com/read/cv43482907/
https://www.bilibili.com/opus/1127331677171875875
https://www.bilibili.com/read/cv43482903
https://www.bilibili.com/read/cv43482903/
https://www.bilibili.com/opus/1127331651421995049
https://www.bilibili.com/read/cv43482900
https://www.bilibili.com/read/cv43482900/
https://www.bilibili.com/opus/1127331625637511169
https://www.bilibili.com/read/cv43482898
https://www.bilibili.com/read/cv43482898/
https://www.bilibili.com/opus/1127331599879241764
https://www.bilibili.com/read/cv43482896
https://www.bilibili.com/read/cv43482896/
https://www.bilibili.com/opus/1127331578375045121
https://www.bilibili.com/read/cv43482895
https://www.bilibili.com/read/cv43482895/
https://www.bilibili.com/opus/1127331552598949892
https://www.bilibili.com/read/cv43482846
https://www.bilibili.com/opus/1127330307053191169