Hacker News Reader

I didn't see mention of conjugate gradients, Newton iteration, or quasi Newton.

And I saw no mention of constraints.

This is primarily in regard to deep neural nets, where second-order methods are too expensive (O(p^2) in parameters, where p is on the order of millions).

I'm not sure conjugate gradient methods are used much, due to the non-convexity of the merit functions, and hard constraints aren't used much either.

quasi newton methods are not square in the dimension of the problem (think limited memory L-BFGS), and can be run in linear time. In my experience, however, they're 2-3 times slower than regular methods like ADAM.

you might call AdaDelta quasi-Newton: the inspiration for it comes from Newton's method.

Reply on news.ycombinator.com