MadChess 3.0 Beta Build 084 (History Heuristics)

I increased the playing strength of MadChess 3.0 by improving the history heuristics used by Late Move Reductions (LMR). First, I added a flag that indicates if a move was played during search (indicated below with “!”). This implies the move is legal (doesn’t expose own king to check) and search examined it (as opposed to moves appearing in the move list after a move that causes a beta cutoff). Moves are encoded as ulong primitives like so: Next, I altered the search function to flag played moves. Then I modified the search function so it not only increments move… Continue Reading

MadChess 2.0 Beta Build 040 (History Heuristic + Late Move Reductions)

I added a history heuristic and late move reductions to MadChess 2.0 Beta. When a move causes a beta cutoff, the move’s history value is incremented by the distance to the horizon squared. (Distance to the horizon squared is used to prevent moves deep in the search tree from having too much influence over move order.) A history value is saved for each combination of piece type and move destination square. Moves are ordered by their history values descending (after cached best move, capture victim, capture attacker, promoted piece, and killer moves). The search horizon is reduced for moves that… Continue Reading