"same" padding, "valid" padding和fixed padding的区别

https://stackoverflow.com/questions/47745397/why-use-fixed-padding-when-building-resnet-model-in-tensorflow
https://stackoverflow.com/questions/37674306/what-is-the-difference-between-same-and-valid-padding-in-tf-nn-max-pool-of-t?r=SearchResults

valid padding ==不padding
same padding 尽量凑, 两边凑, 凑的数量不固定
fixed padding 两边只凑一个