代码如下：
>>>class_num = 10
>>>batch_size = 4
>>>label = torch.LongTensor(batch_size, 1).random_() % class_num
3
0
0
8
>>>one_hot = torch.zoros(batch_size, class_num).scatter_(1, label, 1)
0 0 0 1 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 0
以10类别分类为例，lable=[3] 和label=[0, 0, 0, 1, 0, 0, 0, 0, 0, 0]是一致的.
Tensor.scatter_(dim, index, value)
从 value 中拿值，然后根据 dim 和 index 给自己的相应位置填上值
