A Dimensionality reduction technique similar to a regular Principal component analysis, but it can work with non-linear relations.
There are multiple methods for doing this. Here is one I prefer.
error to your features.error into 1 value, and another that turns that 1 value into error. This step is essentially an auto-encoder.error, this becomes the new error.This gives us something like a PCA, or a greedy autoencoder.