you are right. you are using the output of the previous sparse solution as input into the new one, i.e. stacking sparse coders. Your second question of why thi

you are right. you are using the output of the previous sparse solution as input into the new one, i.e. stacking sparse coders. Your second question of why this is a good idea is the million dollar question. Its pretty much "lets try it and see", with some heuristic reasoning thrown into the mix (its mirrors the brain, it abstracts information, etc, etc). btw, I don't think people use early stopping anymore. It's been replaced by more powerful forms of regularization, such as dropout. The deep learning world is getting more tame, and that makes me happy.