state = tf.Variable(0)
new_value = tf.add(state, tf.constant(1)) update = tf.assign(state, new_value) with tf.Session() as sess: sess.run(tf.global_variables_initializer()) print(sess.run(state)) for _ in range(3): sess.run(update) print(sess.run(state))
>>0 1 2 3
tensorflow 裏的一個函數,在作目標檢測(YOLO)時經常用到。python
其中b通常是bool型的n維向量,若a.shape=[3,3,3] b.shape=[3,3] git
則 tf.boolean_mask(a,b) 將使a (m維)矩陣僅保留與b中「True」元素同下標的部分,並將結果展開到m-1維。算法
例:應用在YOLO算法中返回全部檢測到的各種目標(車輛、行人、交通標誌等)的位置信息(bx,by,bh,bw)session
a = np.random.randn(3, 3,3)
b = np.max(a,-1) c= b >0.5 print("a="+str(a)) print("b="+str(b)) print("c="+str(c)) with tf.Session() as sess: d=tf.boolean_mask(a,c) print("d="+str(d.eval(session=sess)))
>> a=[[[-1.25508127 1.76972539 0.21302597] [-0.2757053 -0.28133549 -0.50394556] [-0.70784415 0.52658374 -3.04217963]] [[ 0.63942957 -0.76669861 -0.2002611 ] [-0.38026374 0.42007134 -1.08306957] [ 0.30786828 1.80906798 -0.44145949]] [[ 0.22965498 -0.23677034 0.24160667] [ 0.3967085 1.70004822 -0.19343556] [ 0.18405488 -0.95646895 -0.5863234 ]]] b=[[ 1.76972539 -0.2757053 0.52658374] [ 0.63942957 0.42007134 1.80906798] [ 0.24160667 1.70004822 0.18405488]] c=[[ True False True] [ True False True] [False True False]] d=[[-1.25508127 1.76972539 0.21302597] [-0.70784415 0.52658374 -3.04217963] [ 0.63942957 -0.76669861 -0.2002611 ] [ 0.30786828 1.80906798 -0.44145949] [ 0.3967085 1.70004822 -0.19343556]]
# Constant 1-D Tensor populated with value list. tensor = tf.constant([1, 2, 3, 4, 5, 6, 7]) => [1 2 3 4 5 6 7]
# Constant 2-D tensor populated with scalar value -1. tensor = tf.constant(-1.0, shape=[2, 3]) => [[-1. -1. -1.][-1. -1. -1.]]
tf.linspace(10.0, 12.0, 3, name="linspace") => [ 10.0 11.0 12.0]
w = tf.Variable([[0.5,1.0]]) x = tf.Variable([[2.0],[1.0]]) y = tf.matmul(w, x) init_op = tf.global_variables_initializer() with tf.Session() as sess: sess.run(init_op) print (y.eval()) #tf中顯示變量值需加.eval
>> [[ 2.]]
僅求得y*log(a),未通過求和操做。要求得求和的交叉熵,還要使用tf.reduce_sumdom
tf.ones([2, 3], int32) ==> [[1, 1, 1], [1, 1, 1]]
# 'tensor' is [[1, 2, 3], [4, 5, 6]] tf.ones_like(tensor) ==> [[1, 1, 1], [1, 1, 1]]
input1 = tf.placeholder(tf.float32)
input2 = tf.placeholder(tf.float32) output = tf.mul(input1, input2) with tf.Session() as sess: print(sess.run([output], feed_dict={input1:[7.], input2:[2.]})) #須要以字典方式賦值
》[[ 0. 0. 0.] [ 0. 0. 0.] [ 0. 0. 0.]]
for example:函數
t=[[2,3,4],[5,6,7]],paddings=[[1,1],[2,2]],mode="CONSTANT"學習
那麼sess.run(tf.pad(t,paddings,"CONSTANT"))的輸出結果爲:優化
array([[0, 0, 0, 0, 0, 0, 0],
[0, 0, 2, 3, 4, 0, 0],
[0, 0, 5, 6, 7, 0, 0],
[0, 0, 0, 0, 0, 0, 0]], dtype=int32)spa
能夠看到,上,下,左,右分別填充了1,1,2,2行恰好和paddings=[[1,1],[2,2]]相等,零填充.net
tf.range(start, limit, delta) ==> [3, 6, 9, 12, 15]
norm = tf.random_normal([2, 3], mean=-1, stddev=4)
# Shuffle the first dimension of a tensor
c = tf.constant([[1, 2], [3, 4], [5, 6]]) shuff = tf.random_shuffle(c) # Each time we run these ops, different results are generated sess = tf.Session() print (sess.run(norm)) print (sess.run(shuff))
>>[[-0.30886292 3.11809683 3.29861784]
[-7.09597015 -1.89811802 1.75282788]] [[3 4] [5 6] [1 2]]
參數1--input_tensor:待求值的tensor。
參數2--reduction_indices:在哪一維上求解。
1,函數原型 tf.slice(inputs,begin,size,name='')
2,用途:從inputs中抽取部份內容
inputs:能夠是list,array,tensor
begin:n維列表,begin[i] 表示從inputs中第i維抽取數據時,相對0的起始偏移量,也就是從第i維的begin[i]開始抽取數據
size:n維列表,size[i]表示要抽取的第i維元素的數目
有幾個關係式以下:
(1) i in [0,n]
(2)tf.shape(inputs)[0]=len(begin)=len(size)
(3)begin[i]>=0 抽取第i維元素的起始位置要大於等於0
(4)begin[i]+size[i]<=tf.shape(inputs)[i]
例子詳見:http://blog.csdn.net/chenxieyy/article/details/53031943
learning_rate = 學習率
loss = 系統成本函數
#tf.train.Saver
w = tf.Variable([[0.5,1.0]])
x = tf.Variable([[2.0],[1.0]]) y = tf.matmul(w, x) init_op = tf.global_variables_initializer() saver = tf.train.Saver() with tf.Session() as sess: sess.run(init_op) # Do some work with the model. # Save the variables to disk. save_path = saver.save(sess, "C://tensorflow//model//test") print ("Model saved in file: ", save_path)
>>Model saved in file: C://tensorflow//model//test
tf.zeros([3, 4], int32) ==> [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
# 'tensor' is [[1, 2, 3], [4, 5, 6]] tf.zeros_like(tensor) ==> [[0, 0, 0], [0, 0, 0]]