TensorFlow的基本運算03

佔位符：

import os
os.environ['TF_CPP_MIN_LOG_LEVEL'] = '2'
import tensorflow as tf
'''
TensorFlow中的佔位符placeholder

佔位符是一種特殊的數據結構，相似動態變量
Feed提交數據，Fetch提取數據
'''
a = tf.placeholder(tf.float32,name="a")
b = tf.placeholder(tf.float32,name="b")



c  = tf.multiply(a,b,name="c")
d  = tf.subtract(a,b,name="d")
#變量初始化操做
init = tf.global_variables_initializer()


with tf.Session() as sess:
    sess.run(init)
    #經過feed_dict的參數傳值，按字典格式
    rc,rd = sess.run([c,d],feed_dict={a:[8.0,2.0,3.5],b:[1.5,2.0,4.]})
    print("value of c = ",rd,"value of d = ",rd)