Today I learned, Stockfish moved to neural network on 2023. I knew that it was just a minmax with alpha beta pruning and a really good eval function. Now its not.

> I knew that it was just a minmax with alpha beta pruning and a really good eval function. Now its not.

It is still "just" a minimax with alpha beta pruning, except the eval function is now a neural network. NNUE, to be more specific.

I highly advise anyone who is curious about chess engines, but hasn't heard about NNUE to read about it. I find this technology absolutely fascinating.

The key idea is that a neural network is structured in a way that makes it very cheap to calculate scores for similar positions. This means that during a tree search, each time you advance or backtrack you can update the score efficiently instead of recalculating it from scratch.

Good starting points to read more:

- https://en.wikipedia.org/wiki/Efficiently_updatable_neural_n...

- https://www.chessprogramming.org/NNUE

I mean, it still is. Now it just has a really good neural net-based eval function. Don't be fooled: it's not that stockfish just has "a really good eval function", and that's the only thing that makes it as strong as it is. The actual tree search is _incredibly_ sophisticated, with boatloads of heuristics, optimizations, and pruning methods on top of alpha-beta.