Supporting mat transpose.

[kilasuelika]

mat transpose is very common in scientific computing. If we want to support that, can we write a function in reverse/core/unary.hpp to directly transpose underneath values and adjoints?

I would like to make a PR but I'm not sure if the above idea is correct.

[kilasuelika]

I'm working on a TransposeNode.

[JamesYang007]

Good point! How did I miss such an important operator. I agree transpose should be a separate node rather than a specialization of a unary node. It would be nice to have a separate file for it like transpose.hpp. I intended unary nodes to represent element-wise operations.

Feel free to make a PR also! I'll try to take a look as quickly as possible.