【TensorFlow】测试时BN层每次输出都一样；BN均值方差训练时必须更新！

tf.layers.BatchNormalization有两个参数training和trainable。
training controls whether to use the training-mode batchnorm (which uses statistics from this minibatch) or inference-mode batchnorm (which uses averaged statistics across the training data).
trainable controls whether the variables created inside the batchnorm process are themselves trainable.

在测试的时候，如果设置training=True，由于batch size=1，导致mean=x，（x-mean）=0。所以BN层的输出只剩beta，每次的输出都一模一样。

BN 注意事项：

1. tf.layers.batch_normalization()中参数training=True
2. UPDATE_OPS：
   
   详见：tf.layers.batch_normalization；TENSORFLOW GUIDE: BATCH NORMALIZATION