tensor.gather

The `tensor.gather` function is a method in PyTorch that allows you to gather values from a tensor along a specified axis. It takes two arguments - the `dim` parameter which specifies the axis along which to gather values, and an `index` tensor which specifies the indices of the values to be gathered.

For example, consider a 2D tensor `x`:

x = torch.tensor([[1, 2, 3],
                  [4, 5, 6],
                  [7, 8, 9]])

To gather elements along the second axis (columns), you can use the following code:

indices = torch.tensor([1, 2, 0])
gathered_values = x.gather(1, indices.unsqueeze(1))

Here, `indices` specifies the column indices of the values to be gathered. The `unsqueeze(1)` call is used to add a new dimension to the `indices` tensor, so that it can be broadcasted with the `x` tensor. The resulting `gathered_values` tensor would be:

tensor([[2],
        [6],
        [7]])

This is equivalent to selecting the second element from the first row, the third element from the second row, and the first element from the third row.