Category: Code

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MadChess 3.0 Beta 4b7963b (Remove Aspiration Windows)

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When analyzing a Carlsen versus Vachier-Lagrave game, I noticed MadChess 3.0 Beta struggling to find Magnus Carlsen’s crushing 23rd move, d6, in the following position. In the engine output displayed by the Hiarcs Chess GUI, I noticed MadChess kept restarting its search of ply 18. It indicated it was searching the first move (of 47 legal moves), second move, third move, etc… then would restart searching the first move again, still on ply 18. It restarted searching the first move of ply 18 numerous times. I suspected this was due to search instability caused by aspiration windows: searching a window… Continue Reading

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MadChess 3.0 Beta d143bb5 (Time Management)

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I improved MadChess 3.0 Beta’s time management. I added code that increases MoveTimeSoftLimit, a TimeSpan variable that controls how long the engine examines a position (in a timed game) before responding with its move. The code increases MoveTimeSoftLimit 25% each ply (depth >= 9) if the score decreases at least one third of a pawn from the prior ply. In some engines this is known as “panic time.” The engine notices the score dropping and- to anthropomorphize it- panics like a human chess player would, spending more time than usual searching for a move that prevents its position from crumbling.… Continue Reading

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MadChess 3.0 Beta 2d855ec (Crash Bug)

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I found and exterminated a bug that caused MadChess to crash in about one quarter of one percent of games. I noticed the engine crashes on line 6 of this code in the Board.IsMoveLegal(ref ulong Move) method. First Hypothesis : Illegal Move Causing King Capture? I suspected the crash was caused by kingSquare == Square.Illegal (meaning king not on any square) due to a missing king. Perhaps a move two ply earlier exposed its own king to check, MadChess erroneously considered the move legal, then captured the king the previous ply? If that were true, in the current ply, when… Continue Reading

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MadChess 3.0 Beta 6794c89 (King Safety)

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I added evaluation of king safety to MadChess 3.0 Beta. Because determining the safety of a king’s position involves examining moves that attack squares near the king, I combined it with piece mobility evaluation, which also examines moves. When examining piece mobility, keep a weighted count of attacks on squares ringing the king (16 squares in outer ring and 8 squares in inner ring) with separate weights for attacks by minor pieces, rooks, and queens. In the following code, white moves to squares ringing the black king contribute negatively to black’s king safety. Black moves to squares ringing the white… Continue Reading

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MadChess 3.0 Beta 6f3d17a (Late Move Pruning)

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I added late move pruning to MadChess 3.0 Beta. Quiet moves (not captures, pawn promotions, castling, or check) near the search horizon that are sorted near the bottom of the move list- in order words, “late” moves- are skipped. These moves are “late” because history heuristics have recorded few instances of them causing a beta cutoff. Most likely they are futile (they will not raise the score to alpha), so the engine doesn’t waste time searching them. The search only examines two quiet moves immediately next to the search horizon, five quiet moves two ply from the horizon, up to… Continue Reading