报错：Expected object of type torch.LongTensor but found type torch.FloatTensor for argument #2 ‘target’
criterion = nn.CrossEntropyLoss()
loss = criterion(y_pre, y_train)
这里的y_train类型一定要是LongTensor的，所以在写DataSet的时候返回的label就要是LongTensor类型的，如下
def__init__(self, ...)