I also have trouble with this. It says that the argument of backward should be the gradients w.r.t. the output. But consistently across the documentation it is never mentioned of what the gradient w.r.t. the output (must be a conspiracy to drive me crazy). Clearly you can define the gradient as an operator but then you don’t get numbers (like 1). Can the thing of which you take the gradient w.r.t. the output not be stated concisely? Does it depend on some usecase? If I just have y=f(x) for example how do I derive the 1 that is assumed?