时代变了。使用最新的TF API，可以通过调用tf.losses.cosine_distance进行计算。

例：

import tensorflow as tf
import numpy as np


x = tf.constant(np.random.uniform(-1, 1, 10)) 
y = tf.constant(np.random.uniform(-1, 1, 10))
s = tf.losses.cosine_distance(tf.nn.l2_normalize(x, 0), tf.nn.l2_normalize(y, 0), dim=0)
print(tf.Session().run(s))

当然， 1 - s是余弦相似度！

这将完成工作：

a = tf.placeholder(tf.float32, shape=[None], name="input_placeholder_a")
b = tf.placeholder(tf.float32, shape=[None], name="input_placeholder_b")
normalize_a = tf.nn.l2_normalize(a,0)        
normalize_b = tf.nn.l2_normalize(b,0)
cos_similarity=tf.reduce_sum(tf.multiply(normalize_a,normalize_b))
sess=tf.Session()
cos_sim=sess.run(cos_similarity,feed_dict={a:[1,2,3],b:[2,4,6]})

打印0.99999988