I am trying to access a 3d tensor matrix by 2d matrix. The return should be an 2d matrix too. And the following is what i try to achieve.

```
dim1 = 2
dim2 = 3
dim3 = 4
source = torch.FloatTensor(dim1, dim2, dim3)
source.normal_()
check = zn > 0.0
index = torch.argmax(check, dim=0)
for i in range(dim2):
for j in range(dim3):
ret[i, j] = source[index[i, j], i, j]
```