The optimizers take parameters and their gradients as inputs and apply update rules to them, but the gradients you supply can come from anywhere. Backdrop is th

The optimizers take parameters and their gradients as inputs and apply update rules to them, but the gradients you supply can come from anywhere. Backdrop is the most common way to assign gradients to parameters, but other methods can work too—as long as the optimizer is getting both parameters and gradients, it doesn't care where they come from.