利用tensorflow實現自編碼

1、原理

監督神經網路的本質就是對特徵的不斷學習挖掘的過程，而中間層就可以理解為對上一層特徵的提取，自編碼就是對神經網路中間層的提取，所以我們可以把高維的資料經過幾層對映到低維，在進行還原的過程

2、測試資料

構建2個三維的球，將其對映到2維，檢視資料分布

def make_ball(r = 2,a=0,b=0,c=0):

points = 
for i in range(400):
t = np.random.choice(360)
t2 = np.random.choice(180)
# r = np.random.random() * r
x = r * np.sin(t2 * np.pi / 180) * np.cos(t * np.pi / 180) + a
y = r * np.sin(t2 * np.pi / 180) * np.sin(t * np.pi / 180) + b
z = r * np.cos(t2 * np.pi / 180) + c
return np.array(points)

由於例子的資料比較簡單，所以就只用了1層的隱藏層，這個隱藏層就是我們要提取的主成分了，用梯度下降法進行優化，損失函式用還原資料與原資料的差的均方誤差，最後模型收斂即完成訓練

def build_autoencode(x):

l,w = x.shape
x_input = tf.placeholder(dtype=tf.float32,shape=[none,w])
# decode
with tf.name_scope("decode"):
w,b = init_wb(shape=[w,2])
decode = tf.nn.softplus(tf.matmul(x_input,w) + b)
# encode
with tf.name_scope("encode"):
w,b = init_wb(shape=[2,w])
encode = tf.matmul(decode,w) + b
with tf.name_scope("loss"):
loss = tf.reduce_mean(tf.square(tf.subtract(x_input,encode)))
with tf.name_scope("train"):
train_op = tf.train.gradientdescentoptimizer(1e-3).minimize(loss)
init = tf.global_variables_initializer()
sess = tf.session()
sess.run(init)
for i in range(10000):
sess.run(train_op,feed_dict = )
if i % 100 == 0:
loss_val = sess.run(loss,feed_dict=)
encode_val,decode_val = sess.run([encode,decode],feed_dict=)
print("iter:",i,"loss:",loss_val)
return sess,decode,encode,x_input

import tensorflow as tf

import numpy as np
import matplotlib.pyplot as plt
from matplotlib import cm
from mpl_toolkits.mplot3d import axes3d
def make_ball(r = 2,a=0,b=0,c=0):
points = 
for i in range(400):
t = np.random.choice(360)
t2 = np.random.choice(180)
x = r * np.sin(t2 * np.pi / 180) * np.cos(t * np.pi / 180) + a
y = r * np.sin(t2 * np.pi / 180) * np.sin(t * np.pi / 180) + b
z = r * np.cos(t2 * np.pi / 180) + c
return np.array(points)
points = make_ball()
points2 = make_ball(r=2,a=3,b=3,c=3)
points3 = np.concatenate((points,points2),axis=0)
def plot3d(points):
fig = plt.figure()
ax = axes3d(fig)
ax.plot_trisurf(points[:,0],points[:,1],points[:,2],cmap=cm.jet,linewidth=0.9)
plt.show()
def plot2d(point):
if len(point) > 400:
plt.scatter(point[:400,0],point[:400,1])
plt.scatter(point[400:,0],point[400:,1])
else:
plt.scatter(point[:,0],point[:,1])
plt.show()
def init_wb(shape):
w = tf.variable(tf.truncated_normal(shape=shape,stddev=0.1),dtype=tf.float32)
b = tf.variable(0.,dtype=tf.float32)
return w,b
# 構建自編碼器
def build_autoencode(x):
l,w = x.shape
x_input = tf.placeholder(dtype=tf.float32,shape=[none,w])
# decode
with tf.name_scope("decode"):
w,b = init_wb(shape=[w,2])
decode = tf.nn.softplus(tf.matmul(x_input,w) + b)
# encode
with tf.name_scope("encode"):
w,b = init_wb(shape=[2,w])
encode = tf.matmul(decode,w) + b
with tf.name_scope("loss"):
loss = tf.reduce_mean(tf.square(tf.subtract(x_input,encode)))
with tf.name_scope("train"):
train_op = tf.train.gradientdescentoptimizer(1e-3).minimize(loss)
init = tf.global_variables_initializer()
sess = tf.session()
sess.run(init)
for i in range(10000):
sess.run(train_op,feed_dict = )
if i % 100 == 0:
loss_val = sess.run(loss,feed_dict=)
encode_val,decode_val = sess.run([encode,decode],feed_dict=)
print("iter:",i,"loss:",loss_val)
return sess,decode,encode,x_input
sess,decode,encode,x_input = build_autoencode(points3)
dd = sess.run(decode,feed_dict=)
plot2d(dd[:400])

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