简单神经网络解决二分类问题示例(Tensorflow)
- 定义神经网络的结构和前向传播输出结果
- 定义损失函数以及选择反向传播优化算法
- 生成会话(tf.Session)并在训练数据上反复运行反向传播优化算法
import tensorflow as tf
from numpy.random import RandomState
batch_size = 8
w1 = tf.Variable(tf.random_normal([2, 3],stddev = 1, seed = 1))
w2 = tf.Variable(tf.random_normal([3, 1],stddev = 1, seed = 1))
x = tf.placeholder(tf.float32, shape=(None, 2),name = 'x-input')
y_ = tf.placeholder(tf.float32, shape=(None,1), name = 'y-input')
a = tf.matmul(x, w1)
y = tf.matmul(a, w2)
cross_entropy = -tf.reduce_mean(\
y_ * tf.log(tf.clip_by_value(y, 1e-10, 1.0)))
train_step = tf.train.AdamOptimizer(0.001).minimize(cross_entropy)
rdm = RandomState(1)
dataset_size = 128
X = rdm.rand(dataset_size, 2)
Y = [[int(x1 + x2 <1)] for (x1, x2) in X]
with tf.Session() as sess:
init_op = tf.initialize_all_variables()
sess.run(init_op)
print(sess.run(w1))
print(sess.run(w2))
STEPS = 10000
for i in range(STEPS):
start = (i * batch_size) % dataset_size
end = min(start + batch_size, dataset_size)
sess.run(train_step,\
feed_dict = {x: X[start:end], y_: Y[start:end]})
if i % 1000 == 0:
total_cross_entropy = sess.run(\
cross_entropy, feed_dict = {x:X,y_:Y})
print("After %d training step(s),\
cross entropy on all data is %g" % (i, total_cross_entropy))
print(sess.run(w1))
print(sess.run(w2))