tensorboard快速上手，tensorboard可视化普及贴（代码基于tensorflow1.2以上）

有太多小伙伴问David 9关于Tensorboard的入门了，

我们都知道tensorflow训练一般分两步走：第一步构建流图graph，第二步让流图真正“流”起来（即进行流图训练）。

tensorboard会对这两步都进行跟踪，启动这种跟踪你必须先初始化一个tensorflow的log文件writer对象：

writer = tf.train.SummaryWriter(logs_path, graph=tf.get_default_graph())

然后启动tensorboard服务：

[root@c031 mnist]# tensorboard --logdir=/tmp/mnist/2
TensorBoard 1.5.1 at http://c031:6006 (Press CTRL+C to quit)

即可看到你定义的流图：

GRAPHS中的每个方框代表tensorflow代码中的scope作用域，比如上图就定义了7个作用域：train, cross_entropy, Accuracy, softmax, input, weights, biases. 每个作用域下都可能有一些Variable或者计算操作的Tensor，可以对方框双击鼠标放大：

上图可见，input的scope下有两个placeholder：x-input和y-input.

对应的流图定义代码如下：

with tf.name_scope('input'):
    # None -> batch size can be any size, 784 -> flattened mnist image
    x = tf.placeholder(tf.float32, shape=[None, 784], name="x-input") 
    # target 10 output classes
    y_ = tf.placeholder(tf.float32, shape=[None, 10], name="y-input")

当然，截止目前，我们看到的可视化都是静态的流图可视化。

我们更多需要的是流图训练过程中动态log，现在还没有动态scalars（标量值）数据。所以我们可以定义一些log summary的操作（下面是对cost和accuracy标量打log）：

# create a summary for our cost and accuracy
tf.summary.scalar("cost", cross_entropy)
tf.summary.scalar("accuracy", accuracy)

定义完成后，我们不需要逐条执行上述操作，只需用merge操作一并执行：

summary_op = tf.summary.merge_all()

最后在流图真正流动训练的时候，记得执行，并写入上述操作到log中：

# perform the operations we defined earlier on batch
_, summary = sess.run([train_op, summary_op], feed_dict={x: batch_x, y_: batch_y})
            
# write log
writer.add_summary(summary, epoch * batch_count + i)

add_summary 的第二项是scalar图标坐标中的x轴的值，summary对象计算出的标量是y轴的值：

如果需要复现，可以使用以下完整代码：

import tensorflow as tf

# reset everything to rerun in jupyter
tf.reset_default_graph()

# config
batch_size = 100
learning_rate = 0.5
training_epochs = 5
logs_path = "/tmp/mnist/2"

# load mnist data set
from tensorflow.examples.tutorials.mnist import input_data
mnist = input_data.read_data_sets('MNIST_data', one_hot=True)

# input images
with tf.name_scope('input'):
    # None -> batch size can be any size, 784 -> flattened mnist image
    x = tf.placeholder(tf.float32, shape=[None, 784], name="x-input") 
    # target 10 output classes
    y_ = tf.placeholder(tf.float32, shape=[None, 10], name="y-input")

# model parameters will change during training so we use tf.Variable
with tf.name_scope("weights"):
    W = tf.Variable(tf.zeros([784, 10]))

# bias
with tf.name_scope("biases"):
    b = tf.Variable(tf.zeros([10]))

# implement model
with tf.name_scope("softmax"):
    # y is our prediction
    y = tf.nn.softmax(tf.matmul(x,W) + b)

# specify cost function
with tf.name_scope('cross_entropy'):
    # this is our cost
    cross_entropy = tf.reduce_mean(-tf.reduce_sum(y_ * tf.log(y), reduction_indices=[1]))

# specify optimizer
with tf.name_scope('train'):
    # optimizer is an "operation" which we can execute in a session
    train_op = tf.train.GradientDescentOptimizer(learning_rate).minimize(cross_entropy)

with tf.name_scope('Accuracy'):
    # Accuracy
    correct_prediction = tf.equal(tf.argmax(y,1), tf.argmax(y_,1))
    accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))
    
# create a summary for our cost and accuracy
tf.summary.scalar("cost", cross_entropy)
tf.summary.scalar("accuracy", accuracy)

# merge all summaries into a single "operation" which we can execute in a session 
summary_op = tf.summary.merge_all()

with tf.Session() as sess:
    # variables need to be initialized before we can use them
    sess.run(tf.initialize_all_variables())

    # create log writer object
    writer = tf.summary.FileWriter(logs_path, graph=tf.get_default_graph())
        
    # perform training cycles
    for epoch in range(training_epochs):
        
        # number of batches in one epoch
        batch_count = int(mnist.train.num_examples/batch_size)
        
        for i in range(batch_count):
            batch_x, batch_y = mnist.train.next_batch(batch_size)
            
            # perform the operations we defined earlier on batch
            _, summary = sess.run([train_op, summary_op], feed_dict={x: batch_x, y_: batch_y})
            
            # write log
            writer.add_summary(summary, epoch * batch_count + i)
            
        if epoch % 5 == 0: 
            print "Epoch: ", epoch 
    print "Accuracy: ", accuracy.eval(feed_dict={x: mnist.test.images, y_: mnist.test.labels})
    print "done"

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