tf.reducemean()到底是什么意思？

https://blog.csdn.net/he_min/article/details/78694383

在tensorflow中经常见到reducemean这个api,到底有什么用，到底是对谁求均值？

api中是这样写的：

tf.reduce_mean(input_tensor, axis=None, keep_dims=False, name=None, reduction_indices=None)

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Computes the mean of elements across dimensions of a tensor.
Reduces input_tensor along the dimensions given in axis. Unless keep_dims is true, the rank of the tensor is reduced by 1 for each entry in axis. If keep_dims is true, the reduced dimensions are retained with length 1.If axis has no entries, all dimensions are reduced, and a tensor with a single element is returned.

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直观的翻译就是

根据给出的axis在input_tensor上求平均值。除非keep_dims为真，axis中的每个的张量秩会减少1。如果keep_dims为真，求平均值的维度的长度都会保持为1.如果不设置axis，所有维度上的元素都会被求平均值，并且只会返回一个只有一个元素的张量。

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为了更加清楚的理解其含义，给出一个简单的例子：

import tensorflow as tf

import numpy as np

'''
x = [[1.,2.],[3.,4.]]

print(tf.reduce_mean(x))
print(tf.reduce_mean(x,0))
print(tf.reduce_mean(x,1))
'''
x = np.array([[1.,2.,3.],[4.,5.,6.]])

with tf.Session() as sess:
    #返回所有元素的平均值
    mean_none = sess.run(tf.reduce_mean(x))
    #返回各列的平均值
    mean_0 = sess.run(tf.reduce_mean(x, 0))
    #返回各行的平均值向量
    mean_1 = sess.run(tf.reduce_mean(x, 1))

    print(x)
    print(mean_none)
    print(mean_0)
    print(mean_1)