The 3 knights

3 février 2018

I was just curious, nothing more.  I was asking myself how hard is it to checkmate with 3 knights so I fired up Stockfish (without any tablebase) and was shockingly surprised to see the search results bump up and down showing different « distance-to-mate » !  How can a search at 41 plies deep jump from 43-35-36-28-25-33 plies to mate?!?!?  Does anyone have an answer?

I have checked with Lomonosov tablebases (mate in 17), Syzygy (DTZ 32) and Nalimov tablebases (mate in 17 as well) so it looks like it’s a mate in 33 plies.

So I’m wondering why Stockfish, at 41 plies deep, is not able to stick to a mate-in-33 principal variation all along starting from ply 33 ?

Thoughts?  Explanations?

Alexander Herbstmann

11 octobre 2016

Here’s a very nice study by the chess composer.  Funny enough, Stockfish has to evaluate to 34 plies deep to finally see the win!