model.train 和 model.eval

model.train() ：啓用 BatchNormalization 和 Dropout

model.eval() ：不啓用 BatchNormalization 和 Dropout

固化權重，防止在測試的時候改變

sets the module in evaluation mode.

This has any effect only on certain modules. See documentations of particular modules for details of their behaviors in training/evaluation mode, if they are affected, e.g. Dropout, BatchNorm, etc.

This is equivalent with self.train(False)

https://pytorch.org/docs/stable/nn.html