pytorch文档学习
(1)
torch.gather(input, dim, index, out=None) → Tensor
input是输入tensor;dim维度（二维矩阵，0表示在列的方向，行的索引；1表示在行的方向，列的索引）；index索引
out[i][j][k] = input[index[i][j][k]][j][k] # dim=0
out[i][j][k] = input[i][index[i][j][k]][k] # dim=1
out[i][j][k] = input[i][j][index[i][j][k]] # dim=2
二维矩阵
[[1,2],[3,4]] dim=1 [[0,0],[1,0]] -------------[[1,1],[43]]
在行的方向上[1,2]对应索引[0,0]就为[1,1]
(2)
torch.index_select(input, dim, index, out=None) → Tensor
>>> x = torch.randn(3, 4)
>>> x
1.2045 2.4084 0.4001 1.1372
0.5596 1.5677 0.6219 -0.7954
1.3635 -1.2313 -0.5414 -1.8478
[torch.FloatTensor of size 3x4]
>>> indices = torch.LongTensor([0, 2])
>>> torch.index_select(x, 0, indices)
1.2045 2.4084 0.4001 1.1372
1.3635 -1.2313 -0.5414 -1.8478
[torch.FloatTensor of size 2x4]
>>> torch.index_select(x, 1, indices)
1.2045 0.4001
0.5596 0.6219
1.3635 -0.5414
dim=0时，第一列[1.2045 0.5596 1.3635] 取索引[0,2] 生成[1.2045 1.3635]