Equivalence of slicing tensor in Pytorch/ATen C++

1. You can also use .slice

Tensor::slice(int64_t dim, int64_t start, int64_t end, int64_t step)

auto partial_gates = gates.slice(1, 0, 3).chunk(4, 1); 

---

2. Pytorch 1.5 using Tensor::index and Tensor::index_put_

using namespace torch::indexing;
auto partial_gates = gates.index({"...", Slice(None, 2)}).chunk(4, 1); 

Also supports multimensional indexing

General translation for Tensor::index and Tensor::index_put_

Python             C++ (assuming `using namespace torch::indexing`)
-------------------------------------------------------------------
0                  0
None               None
...                "..." or Ellipsis
:                  Slice()
start:stop:step    Slice(start, stop, step)
True / False       true / false
[[1, 2]]           torch::tensor({{1, 2}})

It's .narrow() from https://github.com/pytorch/pytorch/blob/master/aten/src/ATen/native/TensorShape.cpp#L364

auto partial_gates = gates.narrow(1,0,2).chunk(4, 1);