Resize_ is just a low level construct that makes b a contiguous Tensor with the given size (increasing the storage if needed).
Note that it does not initialize the memory or guarantee re-used of the existing storage. So you can get arbitrary values after calling it.
Resize is not doing slicing!
set_ changes the Tensor and metadata of the Tensor. In this case, you set a new storage, offset, size and stride. And they happen to be what you expect?