BN大法无敌，这博客从效果上分析为何如此牛逼，原理请移步其它blog，这里就不再赘述了
论文 ： Ioffe, S., & Szegedy, C. (2015). Batch normalization: Accelerating deep network training by reducing internal covariate shift. arXiv preprint arXiv:1502.03167.
背景
学习mxnet时，使用AlexNet去分类fashion-mnist数据集
对比，加BN前后的效果
添加BN前的网络设计如下
'''
net.add(nn.Conv2D(96, kernel_size=11, strides=4, activation='relu'),
nn.MaxPool2D(pool_size=3, strides=2),
nn.Conv2D(256, kernel_size=5, padding=2, activation='relu'),
nn.MaxPool2D(pool_size=3, strides=2),
nn.Conv2D(384, kernel_size=3, padding=1, activation='relu'),
nn.Conv2D(384, kernel_size=3, padding=1, activation='relu'),
nn.Conv2D(256, kernel_size=3, padding=1, activation='relu'),
nn.MaxPool2D(pool_size=3, strides=2),
nn.Dense(4096, activation="relu"), nn.Dropout(0.2),
nn.Dense(4096, activation="relu"), nn.Dropout(0.5),
nn.Dense(10))
'''训练的loss 和准确度变化如下
'''
epoch 1, loss 1.3111, train acc 0.508, test acc 0.762, time 41.8 sec
epoch 2, loss 0.6442, train acc 0.760, test acc 0.816, time 39.1 sec
epoch 3, loss 0.5270, train acc 0.804, test acc 0.827, time 39.1 sec
epoch 4, loss 0.4626, train acc 0.830, test acc 0.861, time 39.4 sec
epoch 5, loss 0.4231, train acc 0.846, test acc 0.867, time 39.1 sec
epoch 6, loss 0.3947, train acc 0.857, test acc 0.873, time 39.9 sec
epoch 7, loss 0.3721, train acc 0.865, test acc 0.879, time 58.0 sec
epoch 8, loss 0.3548, train acc 0.871, test acc 0.883, time 39.1 sec
epoch 9, loss 0.3379, train acc 0.877, test acc 0.882, time 39.1 sec
epoch 10, loss 0.3271, train acc 0.881, test acc 0.890, time 39.0 sec
epoch 11, loss 0.3173, train acc 0.883, test acc 0.893, time 39.1 sec
epoch 12, loss 0.3069, train acc 0.887, test acc 0.893, time 39.5 sec
epoch 13, loss 0.2972, train acc 0.892, test acc 0.898, time 39.2 sec
epoch 14, loss 0.2891, train acc 0.894, test acc 0.903, time 39.0 sec
epoch 15, loss 0.2817, train acc 0.897, test acc 0.904, time 39.1 sec
epoch 16, loss 0.2762, train acc 0.898, test acc 0.903, time 39.1 sec
epoch 17, loss 0.2703, train acc 0.901, test acc 0.909, time 39.1 sec
epoch 18, loss 0.2634, train acc 0.904, test acc 0.907, time 39.1 sec
epoch 19, loss 0.2551, train acc 0.906, test acc 0.910, time 39.1 sec
epoch 20, loss 0.2488, train acc 0.908, test acc 0.909, time 39.5 sec
epoch 21, loss 0.2432, train acc 0.910, test acc 0.910, time 39.1 sec
epoch 22, loss 0.2391, train acc 0.912, test acc 0.912, time 39.3 sec
epoch 23, loss 0.2321, train acc 0.914, test acc 0.914, time 39.3 sec
epoch 24, loss 0.2274, train acc 0.916, test acc 0.912, time 39.1 sec
epoch 25, loss 0.2204, train acc 0.918, test acc 0.913, time 39.7 sec
epoch 26, loss 0.2164, train acc 0.920, test acc 0.917, time 39.1 sec
epoch 27, loss 0.2128, train acc 0.921, test acc 0.917, time 39.1 sec
epoch 28, loss 0.2085, train acc 0.923, test acc 0.918, time 39.2 sec
epoch 29, loss 0.2016, train acc 0.925, test acc 0.920, time 39.3 sec
epoch 30, loss 0.1969, train acc 0.927, test acc 0.917, time 39.2 sec
epoch 31, loss 0.1932, train acc 0.928, test acc 0.921, time 39.2 sec
epoch 32, loss 0.1891, train acc 0.930, test acc 0.916, time 39.1 sec
epoch 33, loss 0.1865, train acc 0.930, test acc 0.919, time 39.6 sec
epoch 34, loss 0.1801, train acc 0.932, test acc 0.917, time 39.3 sec
epoch 35, loss 0.1745, train acc 0.934, test acc 0.918, time 39.7 sec
epoch 36, loss 0.1709, train acc 0.936, test acc 0.919, time 39.3 sec
epoch 37, loss 0.1673, train acc 0.938, test acc 0.922, time 39.3 sec
epoch 38, loss 0.1639, train acc 0.939, test acc 0.922, time 39.6 sec
epoch 39, loss 0.1587, train acc 0.940, test acc 0.922, time 39.8 sec
epoch 40, loss 0.1554, train acc 0.941, test acc 0.921, time 39.5 sec
'''添加BN后的网络结构如下:
'''
net.add(nn.Conv2D(96, kernel_size=11, strides=4),
nn.BatchNorm(),
nn.Activation('relu'),
nn.MaxPool2D(pool_size=3, strides=2),
nn.Conv2D(256, kernel_size=5, padding=2),
nn.BatchNorm(),
nn.Activation('relu'),
nn.MaxPool2D(pool_size=3, strides=2),
nn.Conv2D(384, kernel_size=3, padding=1),
nn.BatchNorm(),
nn.Activation('relu'),
nn.Conv2D(384, kernel_size=3, padding=1),
nn.BatchNorm(),
nn.Activation('relu'),
nn.Conv2D(256, kernel_size=3, padding=1),
nn.BatchNorm(),
nn.Activation('relu'),
nn.MaxPool2D(pool_size=3, strides=2),
nn.Dense(4096),nn.BatchNorm(),nn.Activation('relu'),nn.Dropout(0.2),
nn.Dense(2048),nn.BatchNorm(),nn.Activation('relu'),nn.Dropout(0.5),
nn.Dense(10))
'''训练的loss 和准确度变化如下
'''
epoch 1, loss 0.5627, train acc 0.802, test acc 0.867, time 46.9 sec
epoch 2, loss 0.3653, train acc 0.869, test acc 0.898, time 52.3 sec
epoch 3, loss 0.3055, train acc 0.888, test acc 0.907, time 47.6 sec
epoch 4, loss 0.2716, train acc 0.902, test acc 0.914, time 45.8 sec
epoch 5, loss 0.2446, train acc 0.911, test acc 0.919, time 45.7 sec
epoch 6, loss 0.2234, train acc 0.919, test acc 0.912, time 45.6 sec
epoch 7, loss 0.2066, train acc 0.924, test acc 0.907, time 45.6 sec
epoch 8, loss 0.1908, train acc 0.930, test acc 0.923, time 45.9 sec
epoch 9, loss 0.1766, train acc 0.935, test acc 0.929, time 45.6 sec
epoch 10, loss 0.1623, train acc 0.941, test acc 0.930, time 45.5 sec
epoch 11, loss 0.1511, train acc 0.944, test acc 0.925, time 45.7 sec
epoch 12, loss 0.1388, train acc 0.949, test acc 0.929, time 46.2 sec
epoch 13, loss 0.1262, train acc 0.954, test acc 0.910, time 45.3 sec
epoch 14, loss 0.1203, train acc 0.955, test acc 0.930, time 45.7 sec
epoch 15, loss 0.1072, train acc 0.961, test acc 0.920, time 45.4 sec
epoch 16, loss 0.0997, train acc 0.963, test acc 0.932, time 45.6 sec
epoch 17, loss 0.0938, train acc 0.966, test acc 0.928, time 45.9 sec
epoch 18, loss 0.0833, train acc 0.970, test acc 0.930, time 45.7 sec
epoch 19, loss 0.0767, train acc 0.972, test acc 0.926, time 45.3 sec
epoch 20, loss 0.0707, train acc 0.975, test acc 0.935, time 45.5 sec
epoch 21, loss 0.0624, train acc 0.978, test acc 0.936, time 45.8 sec
epoch 22, loss 0.0591, train acc 0.979, test acc 0.934, time 45.5 sec
epoch 23, loss 0.0526, train acc 0.982, test acc 0.932, time 45.2 sec
epoch 24, loss 0.0481, train acc 0.983, test acc 0.930, time 45.6 sec
epoch 25, loss 0.0440, train acc 0.985, test acc 0.938, time 45.7 sec
epoch 26, loss 0.0393, train acc 0.987, test acc 0.933, time 46.0 sec
epoch 27, loss 0.0359, train acc 0.988, test acc 0.935, time 45.5 sec
epoch 28, loss 0.0341, train acc 0.988, test acc 0.936, time 45.9 sec
epoch 29, loss 0.0301, train acc 0.990, test acc 0.937, time 51.6 sec
epoch 30, loss 0.0266, train acc 0.992, test acc 0.937, time 63.5 sec
epoch 31, loss 0.0236, train acc 0.993, test acc 0.921, time 44.8 sec
epoch 32, loss 0.0201, train acc 0.994, test acc 0.938, time 45.2 sec
epoch 33, loss 0.0187, train acc 0.994, test acc 0.939, time 45.3 sec
epoch 34, loss 0.0169, train acc 0.995, test acc 0.939, time 44.4 sec
epoch 35, loss 0.0142, train acc 0.996, test acc 0.938, time 45.0 sec
epoch 36, loss 0.0126, train acc 0.997, test acc 0.937, time 61.0 sec
epoch 37, loss 0.0131, train acc 0.996, test acc 0.936, time 44.9 sec
epoch 38, loss 0.0127, train acc 0.996, test acc 0.937, time 45.0 sec
epoch 39, loss 0.0116, train acc 0.997, test acc 0.939, time 61.0 sec
epoch 40, loss 0.0105, train acc 0.997, test acc 0.937, time 45.2 sec
'''对比两种网络和训练结果可以看出
加了BN之后网络的收敛速度加快了许多