Vasik Rajlich

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Vasik Rajlich [1]

Vasik G. Rajlich, (born 1971 in Cleveland, Ohio)
a Czech-American [2] computer scientist and MIT graduate [3], where his thesis advisor was McAllester in 1993 [4]. Vasik is International Master in chess and primary author of Fritz 15 [5] [6] and Fritz 16, and before, Rybka [7], the former world strongest chess program, which arose that strong end of 2005 [8] [9]. Vasik is married with Iweta Rajlich, a Polish chess International Master and Woman Grandmaster [10] and main Rybka tester [11].

Vasik Rajlich's interpretation of nodes and depth [12] and the Strelka controversy [13] [14] [15] [16] raised suspicions about the initial origin of Rybka 1.0 [17] [18], but Vasik Rajlich categorically denied Rybka 1.0 was based on Fruit [19] [20], as initially confirmed by Chrilly Donninger in 2005 [21] after early rumours [22] and questions [23] arose, but despite confusing Fruit using MTD(f), Donninger claimed Rybka was basically Fruit in 2007 [24]. On January 19, 2011 ICGA president David Levy broached on cloning issues in a ChessVibes column, covering the controversies, where Vasik again confirmed Rybka source is original after he was invited to comment on Zach Wegner’s analysis [25] a few days before Levy wrote his article [26]. In June 2011, the ICGA has disqualified and banned Rybka and its programmer Vasik Rajlich from previous and future World Computer Chess Championships.


Quotes from an Interview with Vasik Rajlich, December 20, 2005 [27], a new age in Computerchess? Two questions by Alexander Schmidt:

20. Alexander Schmidt: The increase in playing strength of the latest chess engines is unbelieveable. We have since some time with Fruit 2.1 by Fabien Letouzey a very strong open source engine. Do you see a relation between the published sources of such a strong engine and the increase of strength in computer chess in general? How much influence do the ideas of Fruit have on the future of computerchess?

Vasik Rajlich: Yes, the publication of Fruit 2.1 was huge. Look at how many engines took a massive jump in its wake: Rybka, Hiarcs, Fritz, Zappa, Spike, List, and so on. I went through the Fruit 2.1 source code forwards and backwards and took many things.

It is a bit of a pity that Rybka won't make the same contribution to the computer chess community, but at the moment I must also think about protecting my secrets. It's the eternal struggle for a computer chess programmer.

21. Alexander Schmidt: We had our first contact when I had questions about a similarity to Fruit in the search, others found similarities in the evaluation. Some people where a little bit suspicious that Rybka could be a clone of the open source engine. In the meantime it is clear that Rybka is no clone but you used ideas of Fruit (I guess all other serious engine programmers had a look at Fruit too). How strong would Rybka actually be if the Fruit code would have never been published?

Vasik Rajlich: It's a good question. I don't want to get too specific about which ideas from Fruit I think are really useful, but they fall into two categories:

1) Very specific tricks, mostly related to search. 2) Philosophy of the engine (and in particular of the search).

Fruit could really hardly be more useful along both of these dimensions. Fabien is a very good engineer, and also has a very clear and simple conception of how his search should behave.

Anyway, if I really had to give a number - my wild guess is that Rybka would be 20 rating points weaker had Fruit not appeared.

See also

Forum Posts

2004 ...

2010 ...

2020 ...

External Links

Part 2, Part 3, Part 4, Part 5, Part 6, Part 7


  1. Vasik Rajlich in 2006, Photo by Iweta Rajlich, CC BY-SA 3.0, Wikimedia Commons
  2. Vasik Rajlich from Wikipedia
  3. Engineer Shocks Chess World from IEEE Spectrum online
  4. Re: To author of Rybka by Vasik Rajlich, CCC, December 17, 2005
  5. Fritz 15 - English Version, ChessBase Shop
  6. Fritz 15 engine - questions and answers by Albert Silver, ChessBase News, January 04, 2016
  7. Welcome to!
  8. Rybka 1.0 beta release - need testers by Vasik Rajlich, CCC, November 30, 2005
  9. Rybka 1.0 Announcement by Vasik Rajlich, CCC, December 05, 2005
  10. Iweta Rajlich from Wikipedia
  11. Rybka team
  12. To Jeroen and interested minds, re. Tiger node count by Christophe Théron, CCC, August 15, 2008
  13. Strelka controversy from Wikipedia
  14. Strelka 2.0 by Vasik Rajlich, January 11, 2008
  15. Fabien's open letter to the community by Tord Romstad, CCC, January 23, 2011
  16. Fabien's open letter to the community by Tord Romstad, OpenChess Forum, January 23, 2011
  17. Rybka 1.0 vs. Strelka by Zach Wegner, CCC, August 19, 2008
  18. Questions for Vas by Zach Wegner, CCC, August 25, 2008
  19. Is Rybka a derivative of Fruit?, Rybka Forum, July 14, 2007
  20. question to vas on similarity of rybka 1.0 to fruit, Rybka Forum, August 25, 2008
  21. Rybka uses PVS and not MTD(f). Its no Fruit-Clone by Chrilly Donninger, CCC, December 12, 2005
  22. Is Rybka a fruit clone? by Ziad Haddad, CCC, December 06, 2005
  23. Rybka - How much Fruit is inside? by Daniel Mehrmann, CCC, December 11, 2005
  24. Re: I know something of Dr.Donninger by Harvey Williamson, Hiarcs Forum, October 16, 2007, quoted with the kind permission of Chrilly and Enir
  25. Rybka/Fruit: evaluation by Zach Wegner, 2010
  26. Attack of the clones | ChessVibes by David Levy, 19 February, 2011
  27. Interview with Vasik Rajlich by Christopher Conkie, Michael Diosi, Frank Quisinsky & Alexander Schmidt, December 20, 2005, hosted by Ed Schröder (Wayback Machine)
  28. Vasik Rajlich responds to his accusers by Nelson Hernandez, Rybka Forum, July 12, 2011
  29. Luke skywalker has done it again by Daniel Shawul, CCC, April 02, 2012
  30. The ChessBase April Fools revisited, ChessBase News, April 10, 2012
  31. April Fools' Day from Wikipedia

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