Sunday, November 4, 2012

Houdini Chess Engine

Houdini 3: The Best Got Even Better!

The new Houdini 3 contains many evaluation and search improvements in all phases of the game and is about 50 Elo stronger than its predecessor Houdini 2. The opening improvements are mostly related to piece activity and space management and are convincingly demonstrated by the progress in Fischer Random Chess for which Houdini 3 has become about 75 Elo stronger. In the middle game Houdini 3 has significant enhancements for recognizing pieces with limited mobility and in king-side safety. In end games Houdini 3 will seek deeper and solve more positions than before.

Three Long Time Control Challenges As a serious challenge for the new Houdini 3, last month three long matches between the Houdini 3 Beta version and other top engines (Houdini 2.0c, Stockfish 2.3.1 and Komodo 5) were played. Each match consisted of 120 games at 90 min + 30 sec/move, starting from 60 Noomen opening positions played from both sides. Over-all result: Houdini 3 scored 62% (Perf: +81 Elo ± 24 Elo) against the average of Houdini 2.0c, Komodo 5 and Stockfish 2.3.1. Download all the Games The final Houdini 3 Release version is even slightly stronger than the Beta version used in these matches.

In the new Tactical Mode Houdini 3 will adapt its search strategy to prefer tactical solutions rather than positional moves in the root position. Some clever search tricks transform the engine into the most proficient tactical position solver ever. In tactical test suites the Tactical Mode will find more solutions and provide significantly faster solution times. The Accelerated Principal Variation Search or “Smart Fail-High” is especially useful in very deep analysis when a different move becomes best at very high search depth. Houdini 3 will apply an automatic depth reduction that often speeds up finding the Principal Variation by a factor of 5 to 10. Besides Nalimov and Gaviota End Game Table Bases, Houdini 3 now also supports Scorpio bitbases. These bitbases are loaded in memory when the program starts (requiring about 300 MB of memory) and are then readily available to the engine. Hash usage has been optimized, improving back-tracking analysis. Houdini 3 Pro will now support hash tables up to 256 GB. The engine evaluations have been carefully recalibrated so that +1.00 pawn advantage gives a 80% chance of winning the game against an equal opponent at blitz time control. At +2.00 the engine will win 95% of the time, and at +3.00 about 99% of the time. If the advantage is +0.50, expect to win nearly 50% of the time. Fun fact: Over 10 million chess games were played for the development and tuning of Houdini 3!

Version History

For a detailed list of the corrections and features in the new Houdini 3, see the Version History page.
Houdini 3
  • Houdini 3 (20121015): Major new version. Improved search and evaluation (+50 Elo), Tactical Mode, Scorpio bitbases.

Houdini 2
  • Houdini 2.0c (20111120): Maintenance update with minor bug corrections and new analysis options.
  • Houdini 2.0b (20111007): Maintenance update with minor bug corrections and Nalimov EGTB support.
  • Houdini 2.00 (20110901): Improved analysis capabilities, enhanced search and evaluation.

Houdini 1.5
  • Houdini 1.5a (20110115): Maintenance update with work-arounds for Fritz GUI and other minor improvements.
  • Houdini 1.50 (20101215): Improved search and evaluation. Gaviota Table Base Support.

Houdini 1.0
  • Houdini 1.03a (20100717): Bug fix for Multi-PV.
  • Houdini 1.03 (20100715): Multi-PV, searchmove and large page support. Improved evaluation function.
  • Houdini 1.02 (20100618): SMP and hash collision bug fixes. Work-around for Shredder GUI.
  • Houdini 1.01 (20100601): Bug fixes. Improved search algorithm.
  • Houdini 1.00 (20100515): First release.


An invaluable resource for any chess engine author is the excellent Chess Programming Wiki. Without many ideas and techniques from the open source chess engines Ippolit and Stockfish, Houdini would not nearly be as strong as it is now. The Gaviota EGTB probing code used by Houdini is © Miguel A. Ballicora, the Nalimov EGTB probing code is © Eugene Nalimov and the Scorpio bitbase probing code is © Daniel Shawul. The Houdini 3 development was greatly aided by the kind support of Mr. Ahmed Mansoor.
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