tensorflow中設定隨機種子，可分為兩類，圖級seed和操作級seed,
情況1：當沒有設定圖級seed和操作級seed時，生成的隨機數是隨機的
情況2：當設定操作級seed時，生成的隨機數是同一組隨機數，沒有設定操作級seed的操作，生成的隨機數是隨機的
情況3：當設定圖級seed, 將會生成同一組隨機數，如果設定操作級seed又和情況2相同

  ```python
  a = tf.random_uniform([1])
  b = tf.random_normal([1])
  print("Session 1")
  with tf.Session() as sess1:
    print(sess1.run
 
(a))  # generates 'A1'
    print(sess1.run(a))  # generates 'A2'
    print(sess1.run(b))  # generates 'B1'
    print(sess1.run(b))  # generates 'B2'
  print("Session 2")
  with tf.Session() as sess2:
    print(sess2.run(a))  # generates 'A3'
    print(sess2.run(a))  # generates 'A4'
    print(sess2.run
 
(b))  # generates 'B3'
    print(sess2.run(b))  # generates 'B4'
  ```
  To generate the same repeatable sequence for an op across sessions, set the
  seed for the op:
  ```python
  a = tf.random_uniform([1], seed=1)
  b = tf.random_normal([1])
  # Repeatedly running this block with the same graph will generate the same
 

  # sequence of values for 'a', but different sequences of values for 'b'.
  print("Session 1")
  with tf.Session() as sess1:
    print(sess1.run(a))  # generates 'A1'
    print(sess1.run(a))  # generates 'A2'
    print(sess1.run(b))  # generates 'B1'
    print(sess1.run(b))  # generates 'B2'
  print("Session 2")
  with tf.Session() as sess2:
    print(sess2.run(a))  # generates 'A1'
    print(sess2.run(a))  # generates 'A2'
    print(sess2.run(b))  # generates 'B3'
    print(sess2.run(b))  # generates 'B4'
  ```
  To make the random sequences generated by all ops be repeatable across
  sessions, set a graph-level seed:
  ```python
  tf.set_random_seed(1234)
  a = tf.random_uniform([1])
  b = tf.random_normal([1])
  # Repeatedly running this block with the same graph will generate the same
  # sequences of 'a' and 'b'.
  print("Session 1")
  with tf.Session() as sess1:
    print(sess1.run(a))  # generates 'A1'
    print(sess1.run(a))  # generates 'A2'
    print(sess1.run(b))  # generates 'B1'
    print(sess1.run(b))  # generates 'B2'
  print("Session 2")
  with tf.Session() as sess2:
    print(sess2.run(a))  # generates 'A1'
    print(sess2.run(a))  # generates 'A2'
    print(sess2.run(b))  # generates 'B1'
    print(sess2.run(b))  # generates 'B2'
  ```
  Args:
    seed: integer.
  """