从嵌套作用域中收集变量

下面是使用嵌套的变量范围的单层隐藏层多层感知器（MLP）。

def weight_variable(shape):
    return tf.get_variable(name="weights", shape=shape,
                           initializer=tf.zeros_initializer(dtype=tf.float32))

def bias_variable(shape):
    return tf.get_variable(name="biases", shape=shape,
                           initializer=tf.zeros_initializer(dtype=tf.float32))

def fc_layer(input, in_dim, out_dim, layer_name):
    with tf.variable_scope(layer_name):
        W = weight_variable([in_dim, out_dim])
        b = bias_variable([out_dim])
        linear = tf.matmul(input, W) + b
        output = tf.sigmoid(linear)

with tf.variable_scope("MLP"):
    x = tf.placeholder(dtype=tf.float32, shape=[None, 1], name="x")
    y = tf.placeholder(dtype=tf.float32, shape=[None, 1], name="y")
    fc1 = fc_layer(x, 1, 8, "fc1")
    fc2 = fc_layer(fc1, 8, 1, "fc2")

mse_loss = tf.reduce_mean(tf.reduce_sum(tf.square(fc2 - y), axis=1))

MLP 使用顶级范围名称 MLP，它有两个层，各自的范围名称为 fc1 和 fc2。每一层都有自己的 weights 和 biases 变量。

可以像这样收集变量：

trainable_var_key = tf.GraphKeys.TRAINABLE_VARIABLES
all_vars = tf.get_collection(key=trainable_var_key, scope="MLP")
fc1_vars = tf.get_collection(key=trainable_var_key, scope="MLP/fc1")
fc2_vars = tf.get_collection(key=trainable_var_key, scope="MLP/fc2")
fc1_weight_vars = tf.get_collection(key=trainable_var_key, scope="MLP/fc1/weights")
fc1_bias_vars = tf.get_collection(key=trainable_var_key, scope="MLP/fc1/biases")

可以使用 sess.run() 命令收集变量的值。例如，如果我们想在训练后收集 fc1_weight_vars 的值，我们可以执行以下操作：

sess = tf.Session()
# add code to initialize variables
# add code to train the network
# add code to create test data x_test and y_test

fc1_weight_vals = sess.run(fc1, feed_dict={x: x_test, y: y_test})
print(fc1_weight_vals)  # This should be an ndarray with ndim=2 and shape=[1, 8]