the self.log problem in validation_step()
as doc say we should use self.log in last version,
but the loged data are strange if we change EvalResult() to self.log(on_epoch=True)
Then we check the data in tensorboard, the self.log() will only log the result of last batch each epoch, instead of the mean of them.
That is quite unreliable about this issue, it must be turned back to EvalResult() for correct experiments.