tensorflow dropout

import tensorflow as tf
a = tf.constant([[1.,2.,3.],[4.,5.,6.],[7.,8.,9.]])
a = tf.nn.dropout(a,0.5)
b = tf.initialize_all_variables()

with tf.Session() as sess:
    sess.run(b)
    print(sess.run(a))

输出为：

[[  2.   4.   6.]
 [  8.  10.   0.]
 [  0.   0.   0.]]