A Chess Firewall at Zero?
▻https://rjlipton.wordpress.com/2016/01/21/a-chess-firewall-at-zero
State of Computer Chess
Here are some important things to know about chess and computer chess programs (called “engines”).
Chess is hard. Finding a best move in a given position or even telling if you’re winning is a concrete case of a -hard problem.
Computers can now slaughter the best human players on even terms using commodity hardware; the champion Komodo program recently gave substantial handicaps to US champion Hikaru Nakamura and still won.
All leading programs work in progressively deeper rounds of search. Under the common UCI protocol they can be configured to compute a value for each possible move at each depth of search, but in the usual “Single-Line” playing mode they save time by only bounding inferior moves away from the value of their current best move.
Engines often change their “mind” about the values of moves and which one to rank first, but their verdicts become more stable as the search deepens. The values are commonly measured in units of 0.01 called centipawns—figuratively hundredths of a pawn.
Search depth is measured in plies meaning moves by White or Black, so depth 12 means looking ahead 6 moves for both. Programs have a basic search depth that notches up but can extend their search at any time when the critical nature of the moves warrants doing so.
Basic depth 12 was once projected to subdue the human champion; I suspect it’s really depth 18 with today’s programs but no matter: they hit 18 in seconds and reach the high 20s and beyond in games at standard time controls. We recently discussed how closely they are knocking on perfection.
Perfection in chess is probably a drawn outcome, which gets the value 0.00 in centipawns for both players. One way 0.00 values occur during a search is when both players must repeat the same sequence of moves—where any deviation gives that player a negative centipawn value according to the engine. The tendency of engines to give 0.00 at higher depths in positions that look crazy-complicated to human players has been remarked more and more in game commentary by grandmasters in magazines such as New in Chess.
One upshot is that depth of cogitation is solidly quantifiable in the chess setting. We have previously posted about our papers giving evidence of its connection to human thinking and error. The new phenomenon leans on this connection but we will argue that it has a different explanation.
