Claims of Rybka Originality

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Summary of Vasik Rajlich's claims of Rybka Originality.


How much Fruit is inside?


The Rybka source code is original and pre-dates all of the Fruit releases.

Re. your demonstration, the engine scores, pvs and and even first move are all totally different - and that's on a position which you selected. I don't get it.

New Age in Computerchess?

Excerpts from uciengines interview [2]

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.


Is Rybka a derivative of Fruit?


Osipov's speculation is not correct. Rybka is and always was completely original code, with the exception of various low-level snippets which are in the public domain.

Rybka's scores are minimax score - they are propagated up the search tree. In principle, they should be from the tip of the PV, but because Rybka takes the PV from the hash table, this may not always be the case.

Re. depth, this is simply a tool to drive the iterative search. By conventional I mean 'in the normal range'.


Rybka / Fruit


Rybka is of course original (with some accepted exceptions like bit scans & bit counters, etc). Strelka contains Rybka code. Whether Strelka also contains Fruit code, I don't know and don't really care.


Correspondence with Sven Schüle


From: "Vasik Rajlich"

To: "Sven Schüle" Subject: Re: Request for your comments on computer chess topic Date: Sat, 12. Jun 2010 08:32:19

Hi Sven,

yes, these fun topics.

Ippolit is disassembled Rybka 3 with changes. The changes are considerable but not even close to enough to leave any doubt. Robbolito is an evolved Ippolit, with more changes and more cleanup. I haven't checked the other new engines yet.

I'll definitely write up the Ippolit case at some point, for the historical record. Anonymous engines are not accepted by the CC community, so there is no hurry. I think it's best to wait one to two years before writing up an anonymous engine. Otherwise, cloners could use anonymous releases to get information, and then take more aggressive steps.

Re. tracking down the cloners: Not worth the energy, IMO.

Re. Fruit and Rybka: The Rybka source code is original. I did take a lot of things from Fruit, but legally. If there are some good concrete questions from credible people, please send them along.

Re. Rybka 3 source code: Unfortunately, I don't have it. (Yes, it was careless. I'm keeping the Rybka 4 source code.) It's not necessary for writing up the Ippolit case, but it would probably make a court case more difficult.

Best regards, Vas

See also


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