operations in sequence and that includes the things that are really popular today like convolutional networks and recurrent networks but it also includes some of the things that have died out like Bolton machines where we weren't using back propagation today I hear a lot of people define deep learning as gradient descent applied to these differentiable functions and I think that's a legitimate usage of the term it's just different from the way that I use the term myself so what's an example of deep learning that is not gradient