MadChess 3.0 Beta 4d22dec (Endgame Eval Scaling)

I improved MadChess 3.0 Beta’s detection of drawn endgames. The IsPawnlessDraw method scores the following positions as drawn. Though it continues to search moves for a swindle (opponent mistake that makes a drawn game winnable).

• 2N vrs <= 1 Minor
• Q vrs 2B
• Q vrs 2N
• Q vrs Q
• Q vrs R + Minor
• R vrs R + <= 1 Minor
• Q vrs 2R
• 2R vrs R + Minor
• 2R vrs 2R

Testing revealed considering R vrs <= 2 Minors a draw increased evaluation error and caused the engine to play weaker. I left that endgame in the IsPawnlessDraw function as commented out code (explaining the regression) to thwart any temptation to add it later.

In addition, I added a DetermineEndgameScale method that scales down the score of difficult to win endgames.

• Winning side has no pawns and is up by a bishop or less.
• Winning side has a rook or more.
• Winning side has less than a rook.
• Sides have opposite colored bishops and no other pieces.
• All other endgames are scaled by winningPawnCount.

Also, I added a GetTotalScore method that scales down the score as games approach a draw by 50 moves (100 ply) without a capture or pawn move.

Finally The GetStaticScore method brings together the entire evaluation calculation. See the Evaluation.cs source code file for full details. Here’s the code in simplified form.

These code changes increased the playing strength of MadChess 3.0 Beta by 12 Elo. MadChess has crossed the 2600 Elo threshold, at least at bullet chess (2 min / game + 1 sec / move). To date, I have tested MadChess 3.0 Beta exclusively at bullet time control. I was curious how MadChess would perform given more time per game. Of course I’d give its opponents equal additional time. Wouldn’t this benefit both engines equally? Well, chess engines do not scale equally with time. Would MadChess 3.0 Beta or its opponents benefit more from the additional time? Or would it be a wash? That is, they’d scale equally and MadChess 3.0 Beta would achieve the same blitz rating as bullet rating?

MadChess has crossed the 2600 Elo threshold at bullet time control.

It turns out, similar to previous versions, MadChess scales better per time than its opponents. Its blitz chess rating is 2638 Elo. I have started a tournament with rapid time controls (14 min / game + 7 sec / move), however, I won’t know the results for a month or so. Unlike bullet and blitz, I do not have a database of chess engine games at rapid time control. Therefore I cannot run a gauntlet tournament pitting MadChess 3.0 Beta against ten other engines with established ratings. I must run an all-play-all round robin tournament of 48 engines, including MadChess 3.0 Beta, to establish ratings.

MadChess scales better per time than its opponents. Its blitz chess rating is 2638 Elo.

My priority now is to ensure MadChess 3.0 Beta has feature parity (UCI_LimitStrength, MultiPV, etc) with the last release of MadChess, 2.2. Once that’s complete, I’ll release MadChess 3.0.

 

Feature	Category	Date	Commit1	WAC2	Elo Rating3	Improvement
Endgame Eval Scaling	Evaluation	2021 Apr 08	4d22dec	286	2604	+12
Bishop Pair	Evaluation	2021 Mar 14	2960ec9	285	2592	+22
Position Cache Optimization	Search	2021 Feb 23	42d7702	286	2570	+8
Move Generation Optimization	Search	2021 Feb 17	22002dc	287	2562	+12
PVS and Null Move	Search	2021 Feb 09	f231dac	285	2550	+20
Remove Aspiration Windows	Search	2020 Dec 20	4b7963b	290	2530	+9
Time Management	Search	2020 Dec 19	d143bb5	286	2521	+8
Crash Bug	Search	2020 Aug 29	2d855ec	288	2513	+0
King Safety	Evaluation	2020 Aug 16	6794c89	288	2513	+63
Eval Param Tuning	Evaluation	2020 Jul 23	bef88d5	283	2450	+30
Late Move Pruning	Search	2020 Feb 08	6f3d17a	288	2420	+29
Piece Mobility	Evaluation	2020 Feb 01	5c5d4fc	282	2391	+62
Passed Pawns	Evaluation	2018 Dec 27	103	279	2329	+119
Staged Move Generation	Search	2018 Dec 15	93	275	2210	+39
History Heuristics	Search	2018 Dec 03	84	275	2171	+28
Eval Param Tuning	Evaluation	2018 Nov 24	75	272	2143	+47
Sophisticated Search Material and Piece Location	Baseline	2018 Nov 08	58	269	2096	0

1. GitHub commit (hash) or Subversion source code revision (integer)
2. Win At Chess position test, 3 seconds per position
3. Bullet chess, 2 min / game + 1 sec / move