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TensorFlow-Batch_Normalization使用
硬件：NVIDIA-GTX1080
软件：Windows7、python3.6.5、tensorflow-gpu-1.4.0
一、基础知识
1、batch：批量处理（为避免批数据之间差异过大，可通过ExponentialMovingAverage，缓慢改变均值方差）
2、Normalization：归一化（为避免数据之间像素值（0~255）差异过大，激活函数后数据难以有效保存，通过归一化使得处理数据在规定范围内，如-1.0~1.0）
3、处理对象：特征图（权重和偏置？非也！）
4、直观表示：
Wx_plus_b = (Wx_plus_b - fc_mean) / tf.sqrt(fc_var + epsilon)
Wx_plus_b = Wx_plus_b * scale + shift
二、代码展示
import numpy as np
import tensorflow as tf
import matplotlib.pyplot as plt
ACTIVATION = tf.nn.tanh
N_LAYERS = 7
N_HIDDEN_UNITS = 30
def fix_seed(seed=1):
# reproducible
np.random.seed(seed)
tf.set_random_seed(seed)
def plot_his(inputs, inputs_norm):
# plot histogram for the inputs of every layer
for j, all_inputs in enumerate([inputs, inputs_norm]):
for i, input in enumerate(all_inputs):
plt.subplot(2, len(all_inputs), j*len(all_inputs)+(i+1))
plt.cla()
if i == 0:
the_range = (-7, 10)
else:
the_range = (-1, 1)
plt.hist(input.ravel(), bins=15, range=the_range, color='#FF5733')
plt.yticks(())
if j == 1:
plt.xticks(the_range)
else:
plt.xticks(())
ax = plt.gca()
ax.spines['right'].set_color('none')
ax.spines['top'].set_color('none')
plt.title("%s normalizing" % ("Without" if j == 0 else "With"))
plt.draw()
plt.pause(0.01)
def built_net(xs, ys, norm):
def add_layer(inputs, in_size, out_size, activation_function=None, norm=False):
# weights and biases (bad initialization for this case)
Weights = tf.Variable(tf.random_normal([in_size, out_size], mean=0., stddev=1.))
biases = tf.Variable(tf.zeros([1, out_size]) + 0.1)
# fully connected product
Wx_plus_b = tf.matmul(inputs, Weights) + biases
# normalize fully connected product
if norm:
# Batch Normalize
fc_mean, fc_var = tf.nn.moments(
Wx_plus_b,
axes=[0], # the dimension you wanna normalize, here [0] for batch
# for image, you wanna do [0, 1, 2] for [batch, height, width] but not channel
)
scale = tf.Variable(tf.ones([out_size]))
shift = tf.Variable(tf.zeros([out_size]))
epsilon = 0.001
'''
# apply moving average for mean and var when train on batch
ema = tf.train.ExponentialMovingAverage(decay=0.5)
def mean_var_with_update():
ema_apply_op = ema.apply([fc_mean, fc_var])
with tf.control_dependencies([ema_apply_op]):
return tf.identity(fc_mean), tf.identity(fc_var)
mean, var = mean_var_with_update()
'''
Wx_plus_b = tf.nn.batch_normalization(Wx_plus_b, fc_mean, fc_var, shift, scale, epsilon)
# similar with this two steps:
# Wx_plus_b = (Wx_plus_b - fc_mean) / tf.sqrt(fc_var + 0.001)
# Wx_plus_b = Wx_plus_b * scale + shift
# activation
if activation_function is None:
outputs = Wx_plus_b
else:
outputs = activation_function(Wx_plus_b)
return outputs
fix_seed(1)
if norm:
# BN for the first input
fc_mean, fc_var = tf.nn.moments(
xs,
axes=[0],
)
scale = tf.Variable(tf.ones([1]))
shift = tf.Variable(tf.zeros([1]))
epsilon = 0.001
'''
# apply moving average for mean and var when train on batch
ema = tf.train.ExponentialMovingAverage(decay=0.5)
def mean_var_with_update():
ema_apply_op = ema.apply([fc_mean, fc_var])
with tf.control_dependencies([ema_apply_op]):
return tf.identity(fc_mean), tf.identity(fc_var)
mean, var = mean_var_with_update()
'''
xs = tf.nn.batch_normalization(xs, fc_mean, fc_var, shift, scale, epsilon)
# record inputs for every layer
layers_inputs = [xs]
# build hidden layers
for l_n in range(N_LAYERS):
layer_input = layers_inputs[l_n]
in_size = layers_inputs[l_n].get_shape()[1].value
output = add_layer(
layer_input, # input
in_size, # input size
N_HIDDEN_UNITS, # output size
ACTIVATION, # activation function
norm, # normalize before activation
)
layers_inputs.append(output) # add output for next run
# build output layer
prediction = add_layer(layers_inputs[-1], 30, 1, activation_function=None)
cost = tf.reduce_mean(tf.reduce_sum(tf.square(ys - prediction), reduction_indices=[1]))
train_op = tf.train.GradientDescentOptimizer(0.001).minimize(cost)
return [train_op, cost, layers_inputs]
# make up data
fix_seed(1) #make all value of the random data is same
x_data = np.linspace(-7, 10, 2500)[:, np.newaxis]
np.random.shuffle(x_data)
noise = np.random.normal(0, 8, x_data.shape)
y_data = np.square(x_data) - 5 + noise
# plot input data
plt.scatter(x_data, y_data)
plt.show()
xs = tf.placeholder(tf.float32, [None, 1]) # [num_samples, num_features]
ys = tf.placeholder(tf.float32, [None, 1])
train_op, cost, layers_inputs = built_net(xs, ys, norm=False) # without BN
train_op_norm, cost_norm, layers_inputs_norm = built_net(xs, ys, norm=True) # with BN
#define sess
sess = tf.Session()
init = tf.global_variables_initializer()
sess.run(init)
# record cost
cost_his = []
cost_his_norm = []
record_step = 5
plt.ion()
plt.figure(figsize=(7, 3))
for i in range(250):
if i % 50 == 0:
# plot histogram
all_inputs, all_inputs_norm = sess.run([layers_inputs, layers_inputs_norm], feed_dict={xs: x_data, ys: y_data})
plot_his(all_inputs, all_inputs_norm)
# train on batch
sess.run([train_op, train_op_norm], feed_dict={xs: x_data[i*10:i*10+10], ys: y_data[i*10:i*10+10]})
if i % record_step == 0:
# record cost
cost_his.append(sess.run(cost, feed_dict={xs: x_data, ys: y_data}))
cost_his_norm.append(sess.run(cost_norm, feed_dict={xs: x_data, ys: y_data}))
plt.ioff()
plt.figure()
plt.plot(np.arange(len(cost_his))*record_step, np.array(cost_his), label='no BN') # no norm
plt.plot(np.arange(len(cost_his))*record_step, np.array(cost_his_norm), label='BN') # norm
plt.legend()
plt.show()
三、结果展示
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