import tensorflow as tf

sess = tf.Session();

a = tf.placeholder(tf.float32)
b = tf.placeholder(tf.float32)

adder_node = a+b

print(sess.run(adder_node, feed_dict={ a: 3, b:4.5}))
print(sess.run(adder_node, feed_dict={ a: [1, 3], b: [2, 4]}))
#print
#7.5
#[3. 7.]